As suspected 2 of the cylinder head studs didn't appreciate all this repeated activity and promptly pulled through. So the risky business of putting in a thread insert in the 2 stud holes was on the agenda. The tricky bit of this is to ensure all the drilling and threading is done vertically and not on the bonk, otherwise the head won't go on. Because of this I decided to use a drill chuck in the milling machine and setup the cylinder flat on the bed of the mill. As you can see from the first photo managed to fix the cylinder solidly to the bed and then drill and tap for the thread insert. I remember paying a bit of money for my thread insert kit, but it has payed for itself time over especially considering I would be out of the game right now if I had to rely on services from a shop!
Anyway the game plan is to try it again tomorrow with a small amount of gasket silicon on the head gasket, and then if that doesn't work swap the gasket again.
More news tomorrow.