Just in case anyone else was interested, I was able to package the AndyMark 8" wheels (am-0420) into the AM14U3 chassis with only some minor modifications. Still need to figure out if there is a drive belt that will fit correctly, but ground clearances still need to be validated in this configuration.
Same goes for the AndyMark pneumatic 8" wheels (am-0970), but this required much more modification. The inner rails are both moved in by an inch to make room for the wide wheel and these wheels will require some additional spacers for the belt pulleys, different wheel spacers to align them all, longer output shaft for the gearbox, longer axle bolts, longer short churros, shorter inner churros, and a custom plate to replace (am-2954).
What other ideas have people come up with so far?