ORIGINAL: Ricky T
the new era would be easyer to use. and U can use the PS. but your motor will sit way off the chassis
with the traxxas BB, its a little harder to use the PS,, basicly you have to move the trans forward, grind where the Fwheel goes (to make it move forward), and cut the motor mount a little
w/ this you can also use the PS. and the motor sits in the stock place
either one will work.
If you wish to mod, here are some pics for you. Here's my STS .30 setup. With this you can put any engine in with a pullstart too. Drill your trans mounts a little bigger so that you can wiggle it around to mesh the engine gear. But don't move it too far up because the drive shaft won't be long enough. You'll also have to play with the throttle return spring a little and dremel your stock roll cage and some areas of your chassis/mount (for clearance) too. Exactly as Ricky T says.
Downside is that you'll be limited in gearing.