[tommr]

You are right Bill on the Chevy/GMC point. ive always considered the Chevy a GMC product in the larger sense.
The bus rear axle is like the original 4 speed Spicer. Replacement internal parts exist nowhere. The Allison modernized that aspect of the bus. And most of the Allison swap can be retained with an engine update. My guess is that the axle would not handle the torque of a Duramax engine. The 401 had to relocated 6 inches aft and 1.25 inches off center to get a good driveshaft angle. So you need a replacement axle assembly in place before a new engine cradle can be fabricated.
Front suspension has original air brake chambers and they are unique to the Timken steer axle. Bus was garage kept in CA and sat East in a barn for 24 years. We store it inside. Air system up front makes almost no water so those rubber diaphrams are still working. But they cant last forever. Doesn't make sense to be out on the road when they time out so bus is parked. Brake drums for front and rear are not available and it should have 4 new ones. Drums could be hogged out of a piece of iron for crazy $. Modern air chambers could probably be adapted as well with machine work but all of it is expensive and you still have obsolete components. Front needs leaf springs replaced as well as spring eyes. Front is also a little primitive with a buggy spring ride up front. Theres no sway bar system either. A modern steer axle with disc brakes, conventional shocks and a sway bar is very doable. We need a component mfg to help us with dimensional data and maybe some engineering oversight. The guys at SAF Holland have offered some limited assistance with their air beam components but support would not include and actual axle assembly. The aim is to use new components throughout. As I said its all tall order stuff so we need buy in from one of the big axle builders. We have something unique with this vehicle and a unique purpose for it. Tom