I finally managed to get hold of all the bits I needed and in an acceptable condition. The crank that I finally got came from Domiracer in Ohio. It was NOS and not badly priced at all, nor was the postage back to the UK. What did annoy me though was the UK import duty on it. Especially since it had started out here in the first place and was effectively just coming home!
Anyway, I took all the parts over to Rob Wardle in Newcastle who has built me the engine back up, once again with the crankshaft oil feed and timing side bearing conversion. It also had to have a new camshaft and various other bits and pieces, but I finally picked it up on Wednesday and am just in the process of getting it back into the bike. With a bit of luck, I should have it all running nicely again in a week or two!