I managed to do the welding, clean up and tapping OK, but the I ran into some trouble with putting the shoulder on the end. The guys in our workshop took care of it for me, although it even took them a few hours of welding and machining because once you weld it, it won't sit straight in the lathe. Means you can only do one end at a time and it needs a large centre to hold it properly.

Anyway, it's done and I'm very happy with it. Good to prove it could be done. I'm going to paint mine up in Rustseal which is about as rust proof as I can get. Then I'll spray it with Rustguard enamel just to be OTT!
If anyone's desperate for one and can't find a used or new one (such as people like me who live at the far end of Australia!), I could make another one, but be warned, it would have cost me around $300 if I'd had to pay the workshop guys to make it.
Cheers
