[RC-Monster Mike]

I am sorry you had some trouble, Futurespeed. The motor mount was designed to be a direct replacement for the stock part, accounting for the reversed differential. It should fit perfectly with the stock spur gear.
The Kyosho spur is a different manufacturer's part and is slightly different in size - Losi also uses pretty small center diff bearing with a flange, so there isn't a lot of room to account for various manufacturers' spur gears and maintain perfect fit with the stock parts. It has been mentioned already, but we offer hardened steel pinions that can be run directly on the stock steel spur gear, so the Kyosho spur gear isn't necessary with our parts. :)