Hi
I have LPG on my Lexus SC430 with a PRINs system, cost 2k done by professautogas in Coventry, pay the best you get the best. I've had mine for 5 years now serviced every year and never had an issue, great economy, 275 miles out of 60litres, which for a 4.3 is pretty good.
Maintenance is the key!
Hope this helps