I had a 318 Dodge Ram on propane.Watch what you wish for, you might get it!
70 MPH top end, 12 MPG equivalent dollar-wise, and a real hassle to find a station that sold propane on a trip. Plus it didn't run when it got real cold out. Sure, I never had to do anything to the engine, like plugs and such, but I was happy as a clam when I trashed the whole works and put a hi-rise and AFB on it. I wouldn't have another propane setup as a gift!