904 guts in 727 case.

Yep ProTrans does them, over $5K now with shipping. The SS/AH cars used to use them but don't any longer as far as I know. Once they went over 850HP they wouldn't hold up. NHRA rules state any trans that was available in the car is legal. No external modifications are allowed but you can do anything you want to the inside. 340's all came with 727's and of course all big blocks did as well. 360's and 318's could have been equipped either way so a 904 is legal for them.