Alright, personally no matter which brand you use, I highly suggest you do two gear boxes. One on each side, with two small cims into each. It’s a very high powered drive system. Last year we used the andymark single gear gearbox with the two small cims going into each and it was glorious. Depending on what funding would allow I would go with the ability to shift, so you have the power to not be pushed around when your putting tubes on, as well as the speed to get around when you need to. Also i don't know what you are thinking about for wheels, but 4 wheel drive with treaded wheels would be nice, or 6wheel drive with possibly two being omni for turreting, unless you can make your chassis pivot on the center wheels.
All in all, go with two gear boxes total, would be my suggestion, the andymark ones we had last year worked great, and I highly suggest them, the KOP one I assume is probably well done as well.
Good luck
