had gas on my 360 for 5 years now and have a gas carb in place of a holly 4 barrel. performance is great, the engine has mega jolt on it so the ignition curve is set up for lpg. perfomance off road is better than a petrol carb because angles dont bother it, and you cant get watyer in the fuel tank.
you hear allsorts of crap about burned valve seats etc.. which may be true on some engines but cast iron heads couldnt give a toss.
there are alot of crap conversions out there so beware. impco stuff is pretty good for carb sytems or you could go fancy pants multipoint injection (which i would recomend megasquirting to run it then you can use 2 ignition maps for both fuels, and not needing to buy the lpg software would help with the cost).