Not quite the same, but we have an LPG powered forklift at work. It is made by a well known manufacturer of loading equipment and is powered by a well know manufacturer of engines.

When every thing is working it is great, but it is very temperamental. When gas changes from a liquid to a gas it gets very cold and you need a heated regulator to regulate gas flow. If there is the slightest bit of dirt in the cooling system it blocks the heat exchanger and you get no gas and she stops. You need to remember that this is a puka factory job, not a mod.

The 20 kg tank is only good enough for 3 hard hours for a 50hp machine, yours will probably sit in you spare wheel well, so no spare wheel and a small tank. How long that will fuel a V6 car, I would not like to say. With the forklift, the gas is double the price of red diesel, per hour.

Personally unless you use a machine in a confined space and need very low emissions, I'd avoid LPG like the plague.