The rear of the early poncho motors is different from the rear of the later poncho motors. If you were going to run an automatic in your 56 jimmy with that motor it would be easiest to run a HydraMatic. You would have to reinvent the wheel to use a 700R4 or a th350 or th400.

Poncho motors changed around 1961. 1955-1960 bellhousings and transmissions should interchange.