A compression check on all eight cylinders before tear down would have very beneficial, indeed. It’s hard to tell from the picture but I think you were losing fire between the rear three cylinders and even a little from between two and four. The coolant in the valley coincides with the appearance of the head gasket between six and four, and that piston in number four looks to have been getting steam cleaned. I am curious how long you have had the car and what you know about the engine history. That hone pattern looks relatively fresh.
