OK, going back and reading your original post, my best advice would be to do an accurate compression and leakdown test. I have a very specific way I want both done. I do a lot of email tuning for other shops and I have them follow my exact procedures for compression and leakdown testing.
Then, in addition to that, I have them pull the plugs, take a piece of cardboard and poke 8 holes, 2 sets of 4, stick the plugs in the holes and with a sharpy number them on the cardboard. Then take close up pics for me.
That's step 1 and 2. That's going to tell you a lot. I also highly recommend everyone who does this even as a hobby, own a borescope. They're cheap and readily available now.
Step 3 is do a bore scope inspection. Using a cheap USB bore scope, readily available on Amazon, you take pics of the top of the pistons and even the cylinder walls.
I've had a bore scope for probably 15 years now. They were expensive back then. And kinda crappy even for good ones.
This is the one I have now. It's an articulating bore scope that uses your phone for the screen. It's an amazing tool. You can stick in in a spark plug hole and look all around. If you twist it just right you can look back up at the valves.
https://www.amazon.com/Inspection-Ar...hlbWF0aWM&th=1
Following all of these steps will tell you exactly what the mechanical health of your engine is.