If you don't have something real high power and torque I would keep the 904. A 904 is more efficient and will take a lot of power if built right. Some of the same tricks to building up a 727 apply to a 904 such as using thin clutch plates to get more in the carrier, setting clearances and end play, etc... An OD is really nice but their a lot of work (and expense) to install since the floor and crossmember has to be re-worked.
