Cheers for all the replies! Yeh the more I think about it the more I reckon it'd be better to just leave the paint as is as far as possible.
Haydn - I'm not too sure about the paint code but I do know that it had a respray in the 70s, after it had a minor prang. You can see on this photo where the 'new' paint has flaked off. I'm guessing it flaked off when pop backed into it in the shed a couple of years ago.
Mechanically it goes well, it wasn't particularly hard for me to get going - even starting with next to no mechanical knowledge. It still has the original grey in it with ~60,000 original miles on it. I had to replace a few parts in the electrical system (plugs, leads, points, capacitor etc), rebuild the fuel pump and carby, replace master and slave cylinders. I also replaced the welch plugs, the main gaskets and anything else that was rubber while I was at it. Its drivable now, but it did seem pretty hot after I moved it from my old place to my new house - about 10 minutes drive but very hilly. So I'm thinking that either the water pump isn't going as well as it should or the radiator may need recoring.
I'm not in too much of a hurry, it's a long term project and there's a couple of other things I can go on with - so happy to wait if need be.
Cheers
Henry