Propane with a nicely finished hood would be a hit at shows, and after a long day in the cabbage patch. I got a decade more out of tires I thought were shot when I bought the tractor. A Sherman hi low?
Are you sure you don't want to start putting a few afternoons into this project? And I bet you are right about never getting your grand back as is, so go to Wally world and a get a fresh tank... I heard that propane conversions need a lot of tuning to get the same power as factory, I'm sure miner will know more about that. Where are you?