You right gated it, changed oil, etc., before starting it. It started right up but then began running rough, right? I suspect when it was on its side, running very rich, and possibly timing off since none of the engine controls except shutting off the fuel worked, your cylinder head pressures got high enough to stretch the head bolts. Is it possible some felt loose when you removed them? That is a massive amount of coolant yo get into the cylinders assuming you drained everything before removing the head. Have you made the rough check of turning the engine over and verifying all Pistons come to the same height relative to the head? (One or more not coming to the height of the highest would indicate a bent rod or even more serious damage. I'm hoping you get by with only your newly flattened head surface, a new head gasket and head bolts. Since these engines have no sleeves, there is really no way for coolant to get into the cylinders except through the head gasket, and exhaust coming out the radiator confirms that.