Well converted a 421 to run on reclaimed bio gas but the principle is the same if you want to run it off propane here some picyys if you fancy doing it yourself
Spud in must be vac and gas tight or it won't work or it will go bang, whiz, boom.
flue lock out solenoid also very important ( hiss, bang)
Re-wiring the backfire control no petrol no need for it
And thats all folks. Starts and runs on Gas vapour, no need for petrol and have removed the petrol tank for safety no need to have another fuel in the back of the van. you could even run it off a red cylinder if you wanted to, dead handy if theres another fuel protest much easier to have a few of them safely stored away rather than gallons of petrol.