From the fact that this is a C7500 and runs on propane I'm assuming its an old Schwans truck? If it is and has been propane its whole life I'm just wondering why you want to change it? Back when I worked for them the trucks had the 8.1 propane powered big block. They made great power, ran many days of route on 1 tank, and were very easy to refuel. Propane is really not that hard to get. There is a place to refuel in virtually every city and town. The only problem I would see would be 24 hour access to a fill up. But the cost to switch to a fuel that costs more and gives worse mileage might not be worth the trade.