I was looking at brushless revo and castle motor/1515 Neu looked like it was about as big as you can go length wise.. Only reason I ask is that I already have a 1521 and have been trying to get a e-revo roller...
It is a tight fit with the finned can, and I doubt the smooth will be much better. Some of your gearing choices may be limited. And you will have to use the high cg mounting position. Or you could remove the right rear shock and it will fit fine...