Not only is the firing order...
Not only is the firing order different on the 302- and 351W engines, but Ford also numbers its cylinders differently than GM engines.
All's in Order
Many neophyte Ford freaks don't realize that the firing order of the early 351W engine is different from the 221-, 260-, 289-, 302- and late 351W engines. The early 351W's firing order is 1-3-7-2-6-5-4-8, while the smaller Windsor engine's firing order is 1-5-4-2-6-3-7-8. What makes this interesting is that 289/302 cams are completely interchangeable with 351W cams, providing you match the firing order to the camshaft. If a 289/302 cam is used in a 351W engine, the firing order must be changed to the 302 sequence by moving the wires on the distributor cap. The same procedure is used if a 351W cam is used in a 289/302W engine where the firing order in the distributor cap must match the camshaft.
Unfortunately, this trick won't work with sequential EFI engines like the 5.0 if a 351W cam is installed, so be forewarned. According to Kaufmann, switching the plug wires will make the engine run, but power will be down dramatically. The fix is a new ECM to establish the correct injector firing order.
There's no easy visual way...
There's no easy visual way to tell a serpentine-belt-drive water pump from a V-belt water pump unless you remove the rear cover of the pump and look at the the pump impeller vanes. So make sure your pump is correct for the belt-drive-system application.
Engine swapping late-model, serpentine-belt-accessory-drive-equipped engines into earlier cars can also lead to problems if the late-model engine is retrofitted with a standard V-belt pulley drive system. It's easy to overlook the fact that serpentine-belt drives rotate the water pump in the opposite direction from V-belt drive systems. If you equip a late-model 5.0L engine with V-belts without changing the water pump, water pump efficiency will drop radically, and the engine will overheat. The same is true if an early-model engine is equipped with a serpentine-belt drive. The simple fix is to equip the engine with the appropriate water pump for the accessory-belt drive you are using, regardless of engine year.
This is a late-model, four-bolt...
This is a late-model, four-bolt harmonic dampener for a 5.0L engine. Note the position of the TDC mark (1) compared to the crank keyway (2). Earlier three-bolt dampeners will have a different location for the TDC mark. Earlier three-bolt dampeners will have a lighter external balance, too.
Timing Mix 'N' Match
Hot rodders revel in the mix 'n' match form of building a car. Often, parts come from unknown or long-forgotten sources. One source of headaches is Ford's switch from three-bolt harmonic dampeners to four-bolt pulley-mount dampeners around 1968. While that can cause problems in itself, the real challenge comes when the timing marks don't line up. In addition to the pulley-bolt-pattern change, Ford also changed the location of the TDC mark from the left (driver's side) to the right side of the engine. If your timing mark is 90 degrees off, you can change pulleys, change the location of the timing mark indicator or use an aftermarket timing tape to indicate TDC referenced 90 degrees from the original mark.