There are a couple of different LPG systems.
The standard is a mixer system, where gas is injected into the air intake pipe... Its cheap and effective but it has draw backs. Firstly, the flow of gas to each cylinder isnt even... So some get too much, some not enough. It results in poorer economy and your engine wont last as long.
The second system is a gas injection system, where basically the gas is converted from a liquid to gas form and then sent through your fuel rail and through special injectors. This results in more power than petrol, give better economy and is better for your engine.
The best system is liquid injection... where gas is sent to the injectors as a liquid and then converted into gas by the injector. This is advantageous as it means much lower injection temps (suited to forced induction). Also doesnt require a heat converter meaning easier starts. It is the most expensive though.
There are a couple of ways of doing it though... As V6 Commodore engines are very very cheap, its a good idea to use the standard mixer system, then when your engine dies simply change it over (even better if you can do it yourself).
Im seriously considering using the gas injection system (which costs around $3500) as there is no loss of power, it completely replaces the fuel system (so fuel tank/pump can be removed) and should last a lot longer.
If you remove the fuel system, you can often put a gas tank in its place, so you dont lose boot space.