The most common wheelbase is 98mm for racing. This is the wheelbase that comes with the McLaren GTR. I had a chance to build up and test our rental fleet, and they're quick.
Cruizin should have a bunch of motor mounts available. Take into consideration that most alloy mounts will require motors with mounting screws, which the stock motors do not have.
We geared with an 8t, added bearings, carbon t-plate (PN 4 or kyosho medium), PN disc damper and tires (kyosho 20d radial rear, 30d low profile front). The car's were good.
I would advise you to bring the car up to this spec first, and drive it for a while. Then you can change the mount and motor to your liking if you want.