I think I remember that someone several years ago did a run of webber TC heads using modern aluminum (aluminium to you
) and I think it was a Brit company, but unfortunately I don't remember the company. Dave Bean, in the US, used to make webber heads from Stromberg heads. I heard good things about them but he's gone through some changes and I don't know if he still performs the conversion or if he has any finished ones in stock.
After writing a paragraph that probably doesn't help you much, if it were me, I would ask the guys on the lotuseuropa yahoo group. I'll bet someone there would be able to be a lot more helpful than I've been!