Code P0302

Hello, since you have done all that already and you seem to know what you are doing. Because you have covered most bases I would do a smoke test of the Intake, with the exhaust blocked, the throttle body blocked, and block off the brake booster, or go into the booster hose with the smoke machine.

With the fuel treatment having been added multiple times I would be concerned the most with the Fuel injector seals, I know you took them out and tested them, But the seals may be causing a vacuum leak. With fuel treatment that strong and not being mixed with gasoline, which would be my first concern. Those seals upper and lower should be replaced. But if you do a good smoke test with a little pressure behind it, I think you'll find they may be leaking. You've checked everything else correctly.

Also, if this vehicle has any kind of fuel pressure regulator or dampener on the fuel rail, I would check that too. A Regulator will have rubber components inside that could have been affected by the STP.
The Fuel pressure spec is 48-50PSI if you want to do a fuel pressure test.

A side note, it's interesting about the coil swap, even though those coils resistance tested good, it sounds like there might be a couple bad ones in the bunch. They might have been stressed too much on the drive to the gas station. STP is strong stuff, I'm surprised it didn't do more damage.
Seeing you did a static compression test, I would also do a cylinder leak down test, just to verify no valves got burned.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Okay. Good thing you mentioned the timing chain, that absolutely should not be that loose. That is causing the valve timing to be off and is dangerous. If that chain jumps off and this engine is an interference engine, the piston will smash the valves. So first, with the timing chain being that far off, I would not run the engine at all anymore until that is fixed. Either the timing chain tensioner has failed, the chain guides have failed or something else under the timing cover has let go. But that needs to be your first priority. The loose chain is throwing off the variable valve timing and literally everything. I'm very surprised you don't have codes for crank/cam correlation yet. But definitely don't run the vehicle anymore.
Now to the pressure coming out of the oil fill cap. That is extreme positive crankcase pressure. Since you replaced the PCV valve I would inspect the rest of the PCV system, the hose is most likely clogged up too if the valve was that bad. The positive pressure is caused by blow-by gases that escape past the piston rings. The PCV system is there to allow that pressure out of the crankcase. If it didn't have that system, that pressure would push out every seal it possibly could. The front main, the rear main. Etc. Any seal that was below the piston rings would be leaking oil like crazy. So, first check would be to make sure the passage is clear through the whole tube all the way to the crankcase. All the pressure right now is coming out of the oil passages in the cylinder head to the valve cover area. If the PCV system is clear and you're really getting that much pressure, the piston rings would be at fault.
The STP in the tank as a fuel substitute was a really bad idea. Those cylinders were probably running extremely hot. Every engine has some blow-by gases, that's normal, No cylinder seals perfectly. But if anything, you should actually be feeling a little bit of vacuum and not pressure. This engines days might be limited now.
But everything is going to be off at this point with the timing chain being that loose. So, if it's just the timing chain tensioner that went bad, you can try replacing that, get the valve timing where it should be. Do an oil change, because the oil is definitely contaminated badly now. Fill the tank with fresh gas and see how it runs. Thats the best you can do at this point. If the piston rings were heated to a point where they are not sealing anymore, you know where that leaves you unfortunately.
It's hard to say exactly how much damage this did, but it sounds like it might be bad.
I'm looking at the specs for compression right now and I'm sorry to say that the Standard spec is 200-250 PSI, with a minimum of 156 PSI. But again, the valve timing is off, so the compression reading is going to be off as well.
So, I wouldn't go doing an entire timing chain kit, I would just do a tensioner or whatever it needs to just tighten up the chain. And go from there. It's very low on compression, you can see by the wet compression test you gained 10-15 PSI, but still, that doesn't even bring it close to minimum spec. So do your best with the chain issue first. I don't know how it's not throwing more codes, possibly from not driving through certain drive cycles, but I am sorry for the bad news.