We had a convertor made to mate large register crank to early trans...or basically new case with old 19 spline internals. Iir
Not sure if new would fit in old case, dont think theres room in the snout.
For that, a new converter is not required, just use an adapter ring it the end of the crank (I sell those). To go the other way (67 older engine to 68 newer trans) requires a custom converter, or putting the early front parts in the late trans.
