As a long time 4.6 LPG conversion user, I think you have probably arrived at the right answer with the priorities that you have.
Although, my LPG set up has not been any trouble, it can have consequences for servicing, choice of insurer, Channel Tunnel etc. While GB was chancellor/prime minister I used to get a vicarious pleasure when filling up, thinking of all the tax I was denying him, but now even that pleasure has been taken away:5breddevil: - and the proportionate saving between petrol and LPG has been eroded. Back in 2005, I was filling up in ASDA and Morrisons for 29.9p/litre - a full 1/3 of the price of unleaded. Now I am lucky to find LPG at less that 75p/litre.
That said, personally, I wouldn't swap my V8!
Steve