Here are three basic types of manual shift overdrive transmissions for classic and late-model Mustangs with sixes and small-block V-8s. From left to right: Tremec T-5 five-speed, TKO five-speed, and T-56 six-speed. No modifications are required for the T-5 and TKO transmissions aside from special aftermarket crossmembers, available from Mustangs Plus. Some minor transmission tunnel and support structure modifications are required to clear the T-56. Ron Morris Performance has a new bolt-on crossmember for the T-56, available from Mustangs Plus.