[swebster]

Jon,
It actually has more to do with the chassis choice. The Ford 460's came on the Gillig Bus Chassis which was only used on the 370 Classic Motorhomes. Most of the Classic were built on the P30 with the 454 engine. There is one more alternative which is the P30 chassis using an Isuszu Diesel engine or a very rare Cummins setup. One more possibility would be the late model 360 on a Spartan Chassis setup with a Cummins in a Pusher configuration.

Bascially, most of the classics you see are on the P30 with a 454.

(on edit - I see Brett beat me to it....)