British Only; they're in Michigan and will probably have whatever you need. As far as rebuilding your engine check out the upcoming swap meets in the Macon area and plan on attending. From there you can get the name and places of guys who work on the old Brits. In my area here in southern Wisconsin I would recommend Dale's Service; Dale Matteson; dalescycle@hotmail.com. He has a good reputation and I'm sure he would rebuild your 650 to bring it back up to the standards you're looking for. He specializes in Triumphs, BSA'S and Nortons. Has done a lot of work for me on my '71 TR6R Triumph. Very reliable and does a lot of out of state work.
Hope this helps.
Mike