hi David,
to be honest, if I was buying / just bought one then I would book it in for it's first service in my hands, and also ask them to go over it with a fine tooth combe to spot any other issues / potential issues / things to watch with one of the three that I know really know these cars like the back of their hands; The Luti's up in Scotland, Chris Flannigan (Retro Lifetyle I think) or Nick at Austin Garages. If it comes away from one of those three with a clean bill of health then you know you've bought well! You could then use someone more local or continue to use one of those three. But, that's just me and my opinion
There may be others in the same league as the 3 above, but I don't know them or have any experience of them