I believe I can fit an MMM. I'd know for sure if the one I sent to Castle for repair would ever come back
I made the mistake of running aluminum on aluminum on the pinions. That did not last long, even on 4S. I have some RCM Mod1 pinions coming in the mail today. I got a 25t, 23t, and 21t. We'll have to see how well they mesh with each other.
Does anybody forsee and issue with using these?