No mods to the RCM mount necessary. Here is what you have to do: Find a thin 8mm washer that fits on the front side of the center diff rear bearing and you are set. The main problem that I encountered with the kyosho spur was oil leakage. The slot where the o-ring sits is a little wider, which may to blame.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy