[AdamHeard]

If you really want to use 20dp gears for the first stage from AM, you can face down the ones for the first stage to probably 1/8-3/16" (run the Lewis Bending Numbers on them to be sure they are strong enough; There is an excel that is a cheat sheet for them in CD media) to save a lot of weight. Using 32dp would be ideal as you can keep the stock FP pinion for convenience, but then you have to get them hex broached somehow.

I would like to also back up what Cory said about bearings versus bushings. The efficiency losses will be terrible with bushes at those RPMs, and running them out of spec is just asking for unnecessary trouble.