Any suggestions where I might buy the right parts on this side of the pond?

Any custom car shops in your area Martin ? Or Harley dealers ? Otherwise any GM outlet should be
able to help.

The Chevrolets sold in the UK appear to have metric bolt sizes if their
spares & service catalogue is to be believed, but the service guy put
me onto a local industrial fasteners dealer that sold me all the
relevant UNC bolts and a few spares for £3.

Teesside Industrial Fasteners were very helpful! In case anyone else is
stuck:

http://www.applegate.co.uk/company/11/95/477.htm
(just down the road from the Chevvy dealer)

Regards,
Martin Brown