727 transmissions from the 1st cast iron version up to 1966 have 19 splines on the input shaft. Non-lockup 727 transmissions from 1967 onward have 24 splines. Lockup 727 transmissions that debuted in 1978 had 23 splines.  All cases before 1962 were cast iron - the aluminum case came with the 1962 model year.

Not all 727 transmissions made after 1978 were lockup; specifically towing package 727 transmissions commonly were non-lockup, and would have the '67-onward 24 spline input shaft. The A-518 overdrive also has 23 splines. The output shaft has 29 splines.

I just got a 56 2dr with a 1968 roadrunner 383 and 727 transmission.? Since I don't know anything about late 60's mopar, does anyone know if all 727's are the same or?? I would like to get rid of the floor shift and set it up with the push buttons controls on the left dash. Or is this just a bad idea?
thanks in advance                tom