The best bevel single tuner in the country is Nigel Lacey of Weymouth. I have his contact details, but you sound like you dont want quite that level of care
Tony Brancato near Oxford is highly recommended http://www.brancatoengineering.freeserve.co.uk/
John Fallon may have some contacts, but specializes in twins http://www.mdinaitalia.co.uk/
Brian Silver of Moto Marianna near Bracknell is another single specialist, and I can dig out contact details if you need them. Mick Walker has not done any work for many years (if ever himself !), and prefers writing now !
If you think your engine needs any degree of attention to its bevels - do NOT go to a 'good' local mechanic, as anything that goes wrong will be very very expensive to repair.
If you want active contacts, I would post on the Classic Racing message board http://www.crmc.co.uk/