[GeeTwo]

I agree that trying to mount mecanum on a KOP drive system is likely to be far more trouble than it's worth. If you're doing mecanum, save this chassis for an off-season project, or next year. We did mecanum last year, and our construction was rather simple. We used two lengths of 1-1/2" x 1/8" aluminum angle with some notches for the axles on a TB mini, and bolted the TB inside the angle using its existing holes both at the bottom and through the axle plate. We then mounted the hubs "inside" the wheels, and mounted them as close to the gearbox as we could without anything rubbing. We did not support the end of the shaft, and did not have any camber problems. With the extra weight you may be carrying this year, it might be prudent to use taller angle, press a flanged bearing into it, and stand the gearbox back a half inch or so. In that case, I'd use spacers and mount to the holes outboard of the axle plate screws. (We're on a budget and try to never modify a COTS part if we don't have to.)