I myself looked at using the kitbot chassis upside down, but decided against it for the reasons of mounting the gear boxes and the bumpers.
What are you doing for front wheels?
If you could i would recommend you buy 2 more CIMS and do dual CIMS on each side of your robot you will have double the power.
We have 2 more CIMs on the way, and we are using 2" IFI wheels. They get great traction, we have been using them for the past like 4+ years now. The other 2" wheels are on their way with the CIMs