To me... the trans seems pretty much the same for a 2.5 slayer besides the stock gearing being the wide gearset for the two speed. Slayer or revo, I didn't care for that gearset. When I converted to a revo, I replaced the internals with RRP steel and used a standard gearset.
Parts to swap to a revo was:
body
4 pushrods
4 sets of arms
4 outer axles
Spur (38, I think)
CB (15, I think)
revo rear bumper (still using slayer front bumper assembly because it's got more cushion)
That was without the 3.3 chassis, when I got the 3.3 chassis:
2 center axles
1 steering linkage rod
Installed the 2 speed standard offset gears due to not liking the big gap. Removed the rear bumper and got a wing kit, then bolted a revo bumper onto the wing kit... not sure why, but the holes were there and I had a spare bumper. Also ditched the side nerf bars that were there to support the slayer body.
So, you'd still need the nerf bars, front/rear bumper assembly and body. Personally... I thought the body was ridiculous and added a lot more weight to an area the slayer didn't need which raised the COG considerably. Made it more tippy. I replaced the body with a standard truck body and ditched the nerf bars before I converted to a revo.