Hard to say,could peak over 100amps for brief moments,the 9920 would handle it easy.Let us know what you're prepared to spend and your goals and if you need to need to buy batteries and charger aswell.
For the motor mounting thing,there are other ways to mount motors other that motor plates.You could use 2 or 3 of the Bk motor mountings (see pic in this thread
http://www.rc-monster.com/forum/showthread.php?t=1814) and make slots in the chassis for adjustment.I'm doing something similar at the moment for a project with a brass sleeve with mountings silver soldered on.