I just realized I can't do pics, because I got fed up with it last night, and just ripped all the mech. brake stuff out, and mounted everything up for e brakes.
Basically though, it appears as though (and I could be wrong) the tekno neu motors are slightly thicker than the originals, and this is a problem in the muggy. However, with the 18T pinion, the RCM motor spacer still touches the brake calipers to prevent a useable mesh, and the motor can hits the screw that holds the calipers in place anyway.
This is what I did to get to this point: removed the soft pads that you stick on the brake calipers, swapped the screws to shorter button head screws (from socket cap; allows a hair more clearance), removed the screw spacers, and finally, tightened the screws so that I BARELY had any space for the diff to turn freely. Still, after all this, I can't reach a mesh with 18T. I'm guessing 20 may work, but I don't want to go that high, and certainly not all the time. I actually got an 18 and a 12; 18 for bashing/ speed, and 12 for track (not racing).
I wanted to use mech brakes for the alleged better feel, and for the possibility of longer run times, as well as less wear on the motor and esc.