A few have asked for a breakdown of the costs of my DIY install, so I thought I'd post it up.
Tank and filler = Free. I did this by puchasing an old Omega as scrap, which had an LPG setup. I then removed the tank and filler, and stripped the car for what I paid for it.
Front end Voltran sequential kit - £495. This is the Kit from ebay, link has been posted several times.
Also needed to spend £15 on some adaptors, to attach pipes to tank.
So, the bare minimum cost of the install, is £510, if you're prepared to put some knuckle grease into it. This gives you a nicely working sequential gas conversion, using all brand new components bar the tank.
In the end, I opted for using a brand new filler. Reason being, I didn't want to use the old one, as it looked a bit scaby against my nice star silver bodywork.
So a new filler kit cost me around £40, including the rubber bit that is needed for certification.
So for the million dollar question - the cost of my install, in total, was £550.
If you can't source a suitable tank and valve donor, then a new tank kit (inc filler) costs around £200 - so the total cost of that would be £700.
It's always best to allow a bit of leeway, in case you need to buy new plugs, or other little bits, but we didn't have to buy anything extra to do the install.
Strongly recommend changing plugs when it's all apart, looking back!
I didn't have time to do it this time around, but when we get some nice weather, I will pop the filler off, and spray it star silver so it's color coded.
Any questions just post up.