There really isn't an aftermarket one at this time. There are people that are working on it or plan to work on a better design.
I am limited on what I put a 904 into as there are several factors involved, as I've stated.
The best factory 904 sprag is the 1989-1993. It's a 12-element caged bolt in design. But it is specific to the 1989-1993 lockup cases, if you can find one. The L/R drum has a snap ring that retains it to the output shaft support, and there is not an option to add needle bearings in that L/R drum and support at this time--which is the only downfall.
