Sorry for the hijack, don't think my question requires a new thread.
How well do side valves/flatheads run on LPG? I'm thinking about the desoto, I'm going to have to save just to run it to a show :/ getting 8-10mpg on a run, about 6 on the commute to work (hence I can't really afford to use it much )
i would invest in a new or rebuilt carb first, you should be getting a lot more than that
Re the original post, i have a 99 GMC Suburban and a 97 Jeep Cherokee both on LPG.
The Suburban, a 5.7 V8 has a modern multi point system, starts on petrol then switches over after a mile or so. Probably gives me 30mpg cost equivalent, 25mpg when I'm towing my car trailer.
The Jeep, a 4.0 six has an old school, mixer type manual system. It will start on gas or petrol and is great on fuel, averages at least 35mpg cost equivalent. Its a bit lumpy and rough when cold but smooths out after a mile or so, runs better on LPG than petrol
As has been said get the biggest tank you can