You can trim down the revo input shaft so that it is the correct length, and nothing more needs to be done except fit the 3.3spec slipper parts and re-fit the input gear (Im sure the stock gear goes in place without having to drill a new hole on the shaft)...
http://www.rc-monster.com/forum/showthread.php?t=6232
Someone on the traxxas forum did something similar- Im sure you will be able figure something out.