If you already have the NTC motor, then you're dialed into the project. And that will be the only mechanical engine that Cummins makes with enough power for the bus (L10 was a bit lacking). But- If I can make a suggestion- the Big cam is exactly that- BIG and heavy. Actually about 200lb heavier than the Series 60. If I were doing the conversion, I'd look for an M11 or ISM with either the HT740 or HD4060 (World) transmission. I can assure you that there are hundreds of these setups around since this is the engine of choice for most of the trash trucks. The ISM weighs at least 650lb less, is no taller than the 6V-92TA (don't have to modify the floor under the bed), and is not as long as the NTC. In this day and age of politically correctness, having a bus that doesn't smoke is very important-getting worse as time goes on. It is very difficult to makes an NTC not smoke-that's why the electronic N14 was brought out. This so bad that I'm going to put a smoke turbo on my 8V-71N so my engine doesn't smoke at altitude (also want to go to Colorado and be able to climb the hills). If you want to go completely modern and have an engine that weighs in about 1,200lb less than the NTC, the most recent version of the ISL has common rail fuel injection that makes it almost as quiet as a gas engine (sort of weird how quiet it is) and in RV version puts out 400hp with 1,200lb/ft of torque-more than enough power. Always many different ways to go for power. Good Luck, TomC