The RCM diffs are for the revo
You have 2 options:
UE ultralites or VBS
Modified LST2/ muggy diffs
Option 1 is $$$ but will last forever, option 2 is $ but does require a little bit of work- but only a little & will also last forever ( use the metal diff cases and metal collar.. ). Here is an excellent guide:
http://www.rc-monster.com/forum/show...t=9153&page=15