A500 pump gears are the best solution in my mind. Another solution that turbo action uses is to make the converter snout thicker. However this requires the stator support lube dam to be machined off.

I don't think it has anything to do with indexing. There isn't an inherant problem with 904's that 727's wouldn't have. The issue is the diameter of the converter snout (small), that crack from the pump gear load. My guess it happens in race cars more because of the increased pump pressure.