All done. Ran the tap into the valve, cleared out the swarf and regulator fits perfectly. Its now under back seat and I have gas - without having to buy those expensive calor bottles ever again. Just need to connect a hose and refill point once I've used up whats in there.
That said, its full so it could be a very long time (year at least) before its empty.
Some of you will remember I bought this tank on ebay for £26 - full of gas. Just had a hunch it wasn't an LPG tank as described, and I was right - its a vapour rather than liquid tank. I've repainted it since photo below. After that I'll be able to top up on gas at forecourts. Way to go.
