Let's get this straight once and final. Ford Motor Company put T-10 transmissions in Mustangs in 1966. They had, and I will state this again, production problems with top loaders, not enough inventory or an actual structural defect in top loaders, I don't know, but they solved their problem by using the Borg-Warner T-10.Any references to the contrary is plain incorrect. As Ford production documentation was destroyed, the only reference I can make is as stated before, Section 70 page 7 of the Ford Car Parts manual that indicated that T-10 transmissions, marked HEK-AD, were used on Mustangs.
Jim