Johnboy, as far as I know, the chevy gas engines had NV4500's in them up until 2007 in a light truck. The diesels had a ZF6 behind them. Are you stuck on a manual trans? An Allison 1000 series 6 speed would be a nice trans for you. GM had them behind 8.1's in some motorhomes but they were mainly behind duramxes. The gear splits are nice on it and would fit your bus pretty nice I bet.