904 Parts

Unless you are turning it some higher RPM, the wound spring works OK, you can save the 100-120 on that kit. It's RPM that unwinds the spring, not necessarily HP.

You should be able to build a good street strip trans in the 250-300 range depending on how involved you want to get.

I never bother with an upgraded sprag. They aren't really an issue in 904's like in 727's.