yeah my 5.0 V8 is on gas. I bought the car with it on already but I dunno if i'de fork out the cash to get it done. If you work out what you will save it will take you about 3-4 years to get the money back. I find i don't get as good mileage out of my gas as I do with petrol. Get about 350-400kms off a tank of LPG. (and that's a 108Ltr tank under parcel shelf too!) but it only costs about $25 - $30 to fill (80ltr - 80%)
I converted my first car and wouldn't recommend forking out the money to do it.
I ran 16.4 on petrol and 17.0 on gas at heathcote but when i did the gas run I stuffed up and half way down the track backed off the gas
then floored it again.
so there is not much difference performance wise no matter what people say AS LONG AS YOU KEEP IT TUNED! Depends also what system you get. Mine was fitted by ford. Weigh up the pro's and con's cos you do lose a lot of boot space and you can piss off the use of your split fold rear seat too!
hope i was some help
P.S. there some pics of my car at my website below.
ED Farimont 5LTR MPFI V8
Pedders lowing, EL GT 17x8's, ELGT Extractors and 2.5" Exhaust. 3.45 LSD Elec shift kit, full respray with colour coding mirrors, grille, moulds.SVO Boot spoiler, 70mm Herrod MAF, K&N Filter.Built in Pentium III 500, 40GB HDD, 64MB Geforce 4, LCD Screen, IR Remote,Laptop style keyboard, Clarion EQ, Kenwood 4ch, Philips 2ch, Kenwood 6x9's and Kenwood Tornado 12' Subby :D