Personally, I think that you are wrong on several counts.
Frankly, buggering your head gasket from a thermostat fault is questionable. I've done quite a number of heads in the past and the first question that I would raise is whether you removed and replaced the repair with new bolts etc. The next question is whether you 'blued in' the top of your cast iron block 15000 miles ago and whether you have checked the block yet again- on this, the second blow up. As you inform us that you do not possess anything, I would assume to be correct.
You can- or I could- blue in the block and scrape it- assuming that nothing really serious exists but the cheapest and most reliable repair is to have BOTH the block and the head checked and flattened.
Again, at the end of the day- when all is well again, you will need to torque down the head.
Having said all this, the cylinder head might not be strong enough now to stand the weaknesses already created. I've had to be aware of oil ways which are hidden just below the face of the head- and if it is a cast iron block- porosity.
I once skimmed a 12G295 Mini Cooper 998cc block, opened up the ports, reworked and rebalanced the combustion chambers etc for larger valves- and the lot wouldn't turn over. I pulled the plugs, and got an eyeful of glycol from a unseen hole
Read Pete's comments about 'blowing the block' His views are worth digesting.
Norman