I recently rebuilt an early 700 Meteor [1953]. About 800 miles after the rebuild, the left head gasket blew at the innermost part, facing the other cylinder. The other head gasket was also going downhill, due to the heat / flame that was escaping past the blown one. Dark areas on the cylinder heads' gasket faces bore witness to a slight distortion of the gasket faces at this area of the heads - a hot spot where each head is right next to its' neighbour.
I placed some fine emery on a known flat surface and refaced the gasket areas of the heads.
Next came a bonus - I asked, assuming they were available, for solid copper head gaskets - the blown ones had been the copper 'sandwhich' type and they can blow quite easily at times. Solid copper gaskets came, but would not fit. It turned out there were no solid gaskets for the 700 twins, only the 500 Meteor Minor and this is what I had been sent. I had to enlarge the cylinder holes in them, to make them pass over the cylinder spigots [the M.M. 500 has no spigots] and file out the pushrod holes a little and then they fitted. Job done and I doubt it will have any problems with head gaskets again.
That central area, where the two heads meet is a weak and 'hot spot' area, needing special attention. As for torque figures for the head nuts, just tighten them equally and don't overdo it, two of them are only accessible with a spanner anyway.
B.W.