its no big deal to mount the tranny in the revo chassis. you just have to find a good position for it. drilling the holes and just a little dremel work for the spur. my tranny is sitting a tad higher as you can see in one pic above with those yellow washers. so there was very few dremeling for the spur. i have to made a cover to protect it a bit form the dirt.
in the traxxas forum there is a guy who made some sort of tranny holder with two revo chassis braces. that looks good. you may check it.
heres a emaxx tranny mounted in the revo...those motors are for moc-up...i'm going to run V-twin with two maxamps 3s 8000mah lipos...I hope to hit at least 50-60mph http://www.rgcbuilders.net/revo1.jpg