Don't get carried away with the fuel treatments.
Less is more. And, I'm also in favor of not being snobbish when it comes to gasoline. The CR article suggests that it is all the same fuel before the additives are added. The Techron - Complete, in a bottle suggests that you use no more than two bottles between oil changes. The Techron - High Mileage suggests that you can use up to twelve bottles between oil changes, and that it stabilizes fuel for 24-months. Fuel stabilization seems like a good thing, as I often don't drive much, and my fuel vapor system is kinda hacked. Last year, my neighborhood had a couple of Chevron stations, so I got Techron without buying it in a bottle. However, despite the awesome data and reviews, these products are expensive, and they go beyond what the manuals are telling us.
In all three LC 2F heads that I've opened up, they all had a few damaged valve stem seals. But, even when the seals looked good, the intake valves often had black congestion to the point where you wondered about the obvious restriction that was created on the intake-side, if engine vacuum was compromised? Serious engine builders polish ports, so imagine getting your intake-charge past what you see below? The valve stem seal is
supposed to leak a certain amount of oil, otherwise the valve guide and valve stem wear-out. We are working with old technology, but consider modern direct-injection engines, they are notorious for deposits on the intake valves, because fuel is injected directly into the combustion chamber without cleaning polymerizing oil and carbon from intake valves when the engine is running, good guides and stem-seals or not. So, on a LC, you'll need some kind of cleaning-action from the fuel charge to maintain good vacuum. Perhaps just the fuel itself is all that is necessary prevent or remove the deposit, or maybe you are better off with 'top-tier' gasoline, or an occasional bottle of Techron?
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I got off-track, but I started talking about fuel treatments because I was entertaining the possibility of deposits on the piston rings that could compromise their function, and you were considering the possibility that oil was present in the exhaust, or that it was getting into the combustion chamber.
Back to the cooling system, or, if you are going to do a hot-compression test, you'll have to button up everything related to the radiator. I'm curious about what the radiator cap looks like.