Get traxxas brushless diffs, metal primary trans gears, traxxas cvd centers and revo spec plastic shafts or cvd to the wheels. The stock plastic tranny gears will hold for a little while if you convert to a good slipper and set it right. First thing would be the diffs and slipper, the traxxas brushless diffs will hold any bb.
Funny thing is, a picco 26 will stomp alot of big blocks in a maxx.
You can save the hassle of getting a chassis and bb manifold.
I've done the maxx several different ways, but never a true big block. That's what my xxl is for.