Black-Build

Have you allready looked here: http://www.brickshelf.com/cgi-bin/gallery.cgi?m=z32drive ? There some awesome crawlers with great performance out there (especially ''Best crawler yet'' has some awfully good performance) Maybe you can find something and make your own changes?

Okay, but keep in mind you aren't able to go for a little off-road!

You can just stiff up the suspension by putting two instead of one, but i think you allready knew this. If I were you I would consider portal axles with gear reducation, just to make sure there no parts going to break while off-road. But if you wanna keep the drivetrain realistic to the real car, you don't need them. Is there anything else going to be motorized?

It has two in the front and two in the back...

Looks cool, wheelbase a little bit too long but completely understandable if you have two RC-units. About the steering, can't you use servo's or gear up in the chassis? In that case you'll have to place the units two studs up. Whats the gear ratio, 3:1 ?