'65 Barracuda drivetrain swap

Imperial Services lists a conversion cable to use your existing shifter with a later transmission. I don't know if a universal cable can be adapted, but it may be possible. You'll need a speedometer cable housing from a 66, or a custom made housing. You'll need to have a later slip-yoke driveshaft shortened. The later transmission cooler lines might be larger.

Unless you really want a lock-up transmission, the best bet might be to grab the low gear set from the later transmission and install it in the 65 while you rebuild it.