There's a bloke named Dave Hall who does a lot of crank rebuilding for the Classic and Post Classic road racing fraternity around Newcastle. I've never heard anything other than good reports of his work, whether standard rebuilds, or specials with altered strokes etc. I think he may also do re-bores and similar engineering work.
Don't have his number, but ask around and you'll find it for sure. He's well known.
Cheers,
Nitram