Will do.

Anyone know what ones the team guys use?

Okay, quick update...

Got the AE87 and at first it looked the same width as the Tamiya but indeed it is fractions wider (why did I doubt you Jimmy?!?).

The extra width, plus some "ecomony" with the motor shaft depth into the pinion has given me (apparently) sufficient spur/pinion overlap. Fingers crossed.

I will try the ratio suggestions from Fredrik as I now can use my 21 - 23T pinions... :) Will see how ~8 goes instead of 7.0.

@ 4wdfull - Not road tested yet but my X12 motor, Robinson Racing pinion, AE87 spur combination leaves plenty of clearance for the belts - the pinion and belts do not overlap in my install.

Pics of my build to follow in a new thread... am quite pleased with it actually - a gem compared to the 501X.

"djmcnz" - Really looking forward to seeing those pictures. :)