So, at last, the engine is split. The right tool to remove the head bolts, and they've all come away cleanly. Took a trip over to Luton with Janet this morning to get the correct socket, as GSF in Hitchin didn't have stock.
Interestingly, number 3 cylinder was full of coolant. Which isn't a good sign. But does explain the rough running the other week, and, more importantly, the overheating problem. The actual gasket is pretty bad too, looking like it's seen better days. Although no big holes or cracks, which is what I was expecting.
Now starts the job of inspecting the cylinder head for cracks, holes, and warping. Better get the kitchen worktops cleared 
Picture in the extended bit...
