A 727 is bigger and able to handle more torque/HP. But a 904can take a lot also. 904s do have some minor differences when they were installed behind bigger engines - 6 cyl - 318 - 360, (6 cyl. won't bolt up.) But I strongly recommend at least a shift kit and trans cooler for any performance use. There are many parts available which are better than OEM (i.e.: bands, clutches, etc.) so you can have anything between OEM and all-out race. A race 904 can take a LOT of torque/HP, especially when built by a knowlegeable Mopar trans builder. DO NOT use a trans with a "lock-up" converter set up. It limits mods.