It’s finally off – Graham’s “softly, softly – catchy monkey” approach was the winner 
No-one mentioned how bloomin’ heavy they were 
Here’s a couple of photos for your collective amusement – as I’ve not really got much of a clue about what I’d be looking for. There’s no obvious signs of cracks, breaks or tears in the gasket itself. If you see anything amiss, or reckon I need to get a particular thing done – please speak up 
These are cylinders 1 and 2…
…and these are 3 and 4…
I guess I’m going to be busy cleaning stuff next week – I just can’t bring myself to bolt filthy stuff back on
What should I use to do the “decoke”? 7-Up? 
Scotchbrite pad? Brass brush in a drill? Some other gadget?
I’ve done a search, and not really turned up much other than Dave’s advise to grease round the top of the piston whilst decoking them to stop anything slipping down the bores – and to cover the other ones while you do it.
EDIT:
dangerousdave said: All looks ok to me stu, id just decoke the head chambers and the valves and lap the valves in again since its all in bits and you’ll have the springs off to change the stem seals
Also check the top of the bore for a lip, if its only small then its good to go, if its a big ridge then bank on a bottom end rebuild in the near future
And use the grease thing
For the decoke, I would go for wire brush in a drill, maybe get the hoover on the go as well 
Sometimes the valves have some right burnt on deposits that are almost like chalk, if you have a problem getting it off, put the valve in a drill and spin it up and decoke it with some emery cloth taking care to avoid the valve seat area