Been looking for the answer to this question for a long time. A straight forward, simple answer. I'll put out my findings:

Grid RC - Motor Mount for RC8be.
Yay! Great upgrade. What size pinion?

Answer: Mod 1 5mm any tooth (depending your set up) should, SHOULD work.

Here's my choice (19t). http://www3.towerhobbies.com/cgi-bin...0&I=LXXKB4&P=K

OH, and it has to be short shank. At least if your buying the inner mount from what I know.