lpg it.40 quid to fill mine and then still a good 200+ miles depending how i drive with a 60ltr tank in back
Why would you spend money on gas converting a bargain basement 'classic'? Surely the car would have dissolved before the conversion broke even

Interesting thought .. but relatively easy to actually do the sums ... The difference between "projected" petrol costs and "actual" LPG costs, over 53000 miles (5 years) is 10pence/mile (petrol 25 p/mile, lpg 15 p/mile) ... so, once you know the conversion costs, and your average mileage, it is easy to work out the breakeven point.
My - professional - install was £2300 .. so took 23000 miles and 2 years to pay for itself .. so I've already had 3 years and 30000 miles of "profit"
A forum DIY costs around £700 .. so it depend show long it takes you to do 7000 miles ..... obviously ...
You pays your money and makes your choice ... the car "could" go bang or be in an accident well before the breakeven point ... or it could last many years past it ... who knows the future ??