My mate Paul has a 750GT (1973) and a 900SS (1982). He swears by this firm. http://www.mdinaitalia.co.uk/
Also a goo source for parts for the classic bikes should your man get stuck for where to look.
They did a bit of work on his SS for him as it had been lying around for a few years before he bought it, and they got it roadworthy mot'd etc.