Why do I keep blowing head gaskets?
Really? For 13.5? I'd be runnin 116 or 118.
At 13.5:1 he doesn't need O rings or that much octane.
If he is going to do O rings you machine a groove in the head and put the wire in the head.
Then you O ring groove the block and that's the receiver groove. And then that requires dead soft copper gasket to work correctly too. And they have their own set of problems.
So I don't suggest that very often.
When you push a head gasket out like that it's usually a tune up issue. You don't have to see detonation on the plugs to get enough detonation to push the gasket out.
At 13.5:1 the fuel I would use is 100 LL Avgas. It will support more compression than what the OP has.
Without knowing his timing curve, plug heat range, cam timing numbers and such it's hard to say exactly what's going on.