Long story short: I've had enough of throwing good money after bad. I reassembled the engine with new gaskets right through, made sure everything was absolutely squeaky clean before reassembly, checked all surfaces for flatness, followed the assembly instructions for the head gasket very carefully and the bitch is still pissing coolant from around no.1 cylinder. Possibly a cracked cylinder head but I'm not spending a penny more to find out.

PM me.