BB to /6 904

It can be done. You will need a JW Ultrabell bellhousing for 904 to big block. To use it you have to cut the original bellhousing off and the JW bellhousing bolts on top of the pump using longer bolts. I very much doubt the /6 904 will hold up for long behind even a mild big block though. The hardware inside it is not as beefy as a V-8 904. I'm not a trans expert but I think you'd be more likely to succeed with a V-8 904 and having someone who knows a lot about them rebuild it with some tweaks.