I'll put my hand up as a V8 owner who won't recommend LPG. Instead put the money into a 4.6. I bought mine and within 6 months had found the heater core had a leak (when the heater wouldn't work) and that it had dropped a liner.
I originally bought the V8 despite knowing the TD5 would be better on fuel the V8 I know the engine and it's also auto just drive it accordingly. At 80 to 90 it's great on fuel, but only run 98 (and mine prefers shell) and then up to 110 it thirsty again but from 120 on it comes good again. So around the suburban motorways it's 90, out past Dubbo it's 125 +.
Just after doing the head gaskets it kept playing up (with the same symptoms as during the head gaskets) and ended up rebuilding the auto as well which meant I now have a known driveline (moreso now after doing the diffs with Ashcroft lockers as well).
It cost about $3000- all up to source a known low K'm 4.6 from a wrecked P38 and swap over with new gaskets throughout, head & bottom end studs, oil & water pumps etc. Now it goes like it always should have. Gets up to 800k's on the highway, around 450 in the city.
If I had the same issue with a diesel I'm sure I would have been a lot worse off, not only because I couldn't manage to work out the diesel rebuilding but it seems that when one goes it's a lot dearer than a V8 to do and the management of servicing sems to be a bigger deal amongst the diesel crowd.

