OK, Barrels are off, pistons are out!
That last nut was a bugger. I ended up grinding down a ring spanner. The open ended one was doing more harm than good, it had to be a ring spanner.
Pistons look messy, but not too bad. Barrels actually look not too bad to my untrained eye.
Mad pics below - I wish I had something shorter than a 100mm macro lens.
Piston 1:
Piston 2:
Barrel 1:
Barrel 2:
The dust you see in the barrels is just a bit of fluff from the rag - there's no pitting or scratching or anything, just a bit of light marking from the pistons. Crosshatching is good on the front cylinder and fair to good on the top. Barrels are mismatched - B on the top, C on the bottom.
Rest of pics below - shots of all parts from all angles.
http://pictures.1337it.com/index.php?directory=Pistons¤tPic=11
So I'm ready to pull the trigger on a C and a B rebuild kit. Please tell me the barrels are ok.
Will I need anything else?
I'm calling this a lightish seizure and assuming it was from my choice of oil and hopefully not something more sinister, let me know if you concur.