63 904 trans dilemma

A later transmission will have a larger diameter nose on the torque convertor and won't fit the crank pocket (register) on a '67 or older engine.
And no, you can't mix torque convertors between early and late 904s- the input splines are different on the two transmissions.
Early 904s have a ball and trunion output shaft, later 904s use a slip yoke.
Early 904s have a different speedometer drive than later 904s.

By the time you
A.) disassemble the engine to have the crank pocket enlarged by a machine shop
or
B.) have a custom convertor made for the later 904 that has a small nose like the early trans and later model splines

and then buy a new floor shifter and have a new driveshaft made, you will have exceeded the cost of rebuilding the original transmission.