Designed for late-model 5.0 engines, the GT-40 aluminum heads come with thermactor tube openings in each end. Of course, these openings are not needed on early engines, plus they are in the same area where early heads mount accessories up front, like the A/C brackets and alternator bolt. Because the openings are only used at the rear on 5.0s, Ford offers thermactor inserts to plug the holes at the front. The inserts, PN F4ZZ-6E086-A for a package of two, are threaded on the outside and inside, so they also double as bolt holes. You'll need two packages, or four inserts total, to plug the holes for early-model usage.