Re:
Had a proper go at the frame this afternoon. Other than the cable rub all seems perfectly sound. The rub is pretty deep (maybe 75% of the tube thickness!) but at least it's in a part of the frame that won't be under much stress, especially when standing on the pedals (i.e. descending, where it matters most).
I rubbed the frame down with 200 grit wet & dry followed by 600 grit, then gave it a good polish up with the silvo from the cutlery drawer. Took about three hours in total, and I'm quite pleased with the result
The rear swing arm is also in need of TLC. I've rubbed it down and prepped it for a coat of paint, but I'm still mulling over possible paint jobs and ways to build it up, so that'll have to wait a bit.
The rear pivot bearings seem in good nick, but the shock mount hardware is all over the place having been bodged together with the wrong size shock bushes, wrong length bolts without proper washers etc.
It looks like it might be quite difficult (and over priced!) to source a replacement official shock mount kit, so I'll probably improvise something suitable from a local hardware store. I'm sure fleabay will offer a cheap and cheerful suitable replacement shock bush.
The shock itself moves smoothly enough but has been de-pressurised and I don't own a shock pump, so not sure if that will need attention yet. If it's in working order, the £1.04 I paid for the shock and frame was a bit of a bargain!