A-body Hemi box 4 speed

Everything about this trans points to a modified part rather than a factory built transmission. Still a great part to have.

Chevy guy built this for his street strip camaro is what it appears it will fit as is. With a little work it could be used in a A-body.

Your analyzing result backward: Everything about this trans point to a Mopar factory built transmission.

Your theory has a big flaw: If the Chevy guy built this trans for his application, by the time it dis-assembly he would machine the input-shaft, not cut it by chainsaw like this one.