Steve Baur
Former Editor, Modified Mustangs & Fords
November 5, 2014
Photos By: Rusty Gillis, Courtesy of Thoroughbred GT

In the world of classic Mustang restoration, it's no secret that some restoration parts fit better than others. In fact, many people opt to find good used parts to complete their resto project rather than try and work with new parts. It doesn't have to be that way and Thoroughbred GT is here to prove it.

Nathan Miller started working on Mustang restoration projects at the young age of 16, and he eventually opened up his own shop, Buckeye Restoration, in 2001. Throughout his 20 years of experience restoring cars, Miller became increasingly displeased with some of the aftermarket parts and how they fit, and he decided to start assembling his own chassis components for resale.

Embarking on such a project was not an easy undertaking, but it all begins with a solid foundation from which to work from. Originally, Miller and crew tried to reverse engineer the car, but it didn't produce satisfactory results. They had to start from scratch and that doesn't come cheap, in time or investment. The body fixture alone cost over $250,000 and took two years to develop.

Working with Cardinal Precision Machining to build the new fixture, Miller and Cardinal Precision Machining's Steve Ruhl realized that the old way of doing things needed to be revamped. Using computer-aided design (CAD) software, they CNC-machined the fixture points to the factory blueprint specifications.

"Using modern machines, we are able to get tolerances as tight as or tighter than the original, meaning fewer problems for the restorer and end user," Ruhl notes.

"We stand behind our products and are proud of our work," Miller notes. "Thoroughbred offers the best restoration components and assemblies for both the professional and amateur. Our conversions are the best available, and our parts fit properly. We stand behind our products 100 percent."

Now available are coupe-to-fastback conversions, full chassis skeletons, clipster back-halfs (everything from the firewall back), as well as full floor assemblies. Thoroughbred GT offers full replacement floors for '65-'70 coupe and fastback, and '65-'68 convertible Mustangs. In the next six months, they will be introducing the '65 convertible '67-'68 skeletons. The Ohio-based company's mission is to deliver the best possible restoration parts and components available, and we decided to find out how good their stuff is by ordering the company's biggest seller, a new complete floor package for our '69 Mustang SportsRoof project.

For those of you who haven't caught previous installments of the project, we picked up a 302-powered SportsRoof on the cheap and are opting to do everything ourselves to find out how hard it is to accomplish the restoration. We will have the watchful eyes of the Gillis Performance Restorations staff watching over us and offering suggestions as we attempt the floorpan installation, but it'll be up to us to burn in the welds. This month, we wanted to show you what goes into building the floor, and we also begin prepping the SportsRoof for the surgery that you'll find in the second part of this story coming soon. Let's get started.

01. Building a full floor begins with a bunch of smaller pieces that form the rear trunk floor and main seat floorpans. These are set in a jig and welded together to form the panels you see here. The panels then receive a weld-through primer coating; Thoroughbred GT prefers to sand this off where they weld for a cleaner bond. To start the full floor assembly, the seat risers are placed in the main fixture first, followed by the seat and trunk floor assemblies.

02. The new rear framerails are prepped much like the floorpans are, and a few small components are welded on before the framerail is laid in place on the floor.

03. Here, the rear shock tower is prepped and the pinion snubber bracket is welded on before the assembly is welded to the trunk pan.

04. Though no one has ordered a full floor without them, these dual-exhaust pans that are being mocked up are optional. If you’re building a concours six-cylinder, the single may be the way to go, but what fun is that?

05. With all of the sub-assemblies finished and the front supports and rear framerails in place it’s time to spot-weld. The fixture holds everything in place and Thoroughbred GT also uses locking pliers to secure the panels as the staff uses the industrial-spec, water-cooled 250-amp spot welder to bond the panels together.

06. The rear shock tower is next to get welded to the floor. When you buy a complete floor like this, you’re assured that there is no hidden rust underneath panels like these. It’s hidden rust in areas like this that can turn your “good deal” into a money pit.

07. The front floor supports are welded in next, followed by the U-brace. Thoroughbred rosette welds the rear of the transmission tunnel because of the limitations of the equipment, and they also weld up areas of the torque boxes to add strength to the chassis. These are things to consider should you restore a car to concours specifications.

08. Here, the front U-brace location is being verified by a technician. A machinist’s scale is now used to perform this duty, though the bricklayer’s ruler is extremely accurate.

09. With all of the welding complete, the floor is off to the paint booth for a coating of Sherwin-Williams red oxide epoxy primer. Once dry, it is crated up and loaded on a truck to be shipped to its destination.

10. It was brought to our attention that we had not yet reported on removing the drivetrain from our ’69 Mustang project. Gillis Performance Restoration’s new guy, Wilburn Glen Brown, assisted in the removal and manned the engine hoist while this author made sure the transmission cleared the tunnel and firewall. This is not the best way to do things, of course, but it gets the job done.

11. The floor of our ’69 Mustang project was not that bad, all things considered. While the rusty bits would be easily repairable, the passenger rear framerail was bent out of position during a collision. It rests 2 inches higher than normal at the back of the car, and 11⁄2 inches right above the axle. Installing the new Thoroughbred GT floor would fix the rust issues and make it easier to deal with the framerail issue as well. This will give us a solid and square foundation from which to hang the new rear sheetmetal.

12. This is the driver’s-side rear seat where you can obviously see some rust damage, both to the floor as well as the trim panel bracket. Thoroughbred GT includes the brackets on its complete chassis, but they are optional on the full floors and something you’ll need to install yourself. They’ve found that the bracket locations vary depending on where the car was manufactured, so it’s best to take measurements from your original floor and then install the new ones to match.

13. The front of the floorboard, as well as portions of the toeboards, need to be repaired on our car. The passenger side is actually quite weak from a structural standpoint.

14. This is where the brunt of the collision occurred, and while it has largely been pulled out at some point, the horizontal lines moving from bottom left to upper right are where the trunk floor is creased from the collision. There isn’t a straight piece of metal to be found back here, so we’ll be starting fresh atop the Thoroughbred GT floor.

15. We started to remove the factory quarter trim brackets but in the end, we decided to just get new ones. If you have the time and yours are all in good shape, then go ahead and reuse them. We are a bit short of time around here and as pictured earlier, one of the main quarter trim brackets was rusted away. They are spot-welded in, so if you’re going to remove them just clean up the area to find the factory spot-weld locations.

16. In preparation for the removal of the factory floor, we need to remove the seat pans to be able to split the inner and outer rocker panels. We used our Eastwood air drill along with the company’s premium spot-weld cutter.

17. Underneath the seat pans, the floor was in good shape other than some mild surface rust.

18. We’re at the point now where we need to get some square tubing and weld in some supports to the roof and B-pillars. We’ll cover this in the next installment of our ‘69 SportsRoof project, and get the floor installed.

19. It’s here! Obviously an item this big is shipped truck freight, so you’ll need a way to off-load it. As with any package you receive, inspect it for any damage before accepting it.

20. Thoroughbred GT does a great job of crating up the new floor assembly, and you’ll be left with some good wood once you extract the floor from the crate. Get yourself some plywood and you’ve got a workbench! Next time around we’ll have this floor installed and can begin restoring our ’69 Mustang SportsRoof to its former glory.