Pre and post 67 replacement tanks are basically the same pressings these days and can take a little adjustment to clear the bonnet at the front and sometimes the steering damper and coupling underneath, but a few wacks with a rubber mallet usually sorts them out. Most of the usual suppliers, VW Heritage, Megabug etc will sell you a new tank and any old-school body shop or radiator place will be able to patch over the original filler and any unwanted vents etc and will be able to fit your existing filler neck. Brazing is usually better than welding on tanks as it's more gentle on the thin metal and seals better.