Need some opinions on where to go from here...

Alright, so back with an update...

First thing I did while waiting to borrow a good battery (here I was cleaning terminals, meanwhile it was a bad battery that would drop in voltage from 12.5 to 4 in under a minute after taking a charger off of it) was run another leak down test on cylinder number 6 a couple nights ago...As soon as I got it to top dead center, again using my small bore scope, I put the air to it, and it leaked less than 5% like all the other cylinders. So then I backed it up a bit to before TDC and the 70% leak was back....back to TDC and the leak was gone again...a bit past TDC, and it leaked. One more time right back, and all good at least then 5%. So then I added oil to the cylinder just to see what might happen, and readings based on piston position were EXACTLY the same as without the oil, literally made no difference- at TDC all good, just before or after and no bueno. When the leak was at 70% I left the rad cap off and had the cylinder filled for almost 10mins- zero bubbling of water in the rad. No sound out the exhaust, no air out the crankcase, no air out the intake/carb..It just seemed like air kinda at the valves is where the sound was..Also, since it was mentioned, when I did the initial leakdown test, I actually tested each cylinder twice and the numbers all repeated. Only cylinder 6 was the one I had trouble with, but now seems to be alright at TDC.

Today with the good battery in I ran a compression test on the engine, and just like the leakdown, with a completely cold engine. EVERY CYLINDER cranked 155-160psi. When the engine was hot, cylinder 4 was 20psi less, and I could swear the numbers were at 125psi, with cylinder 4 at 100psi, but stupid me, didn't write it down. This is a late 70s 360 with cast flat dish pistons down the hole about .110". With the thin MP head gaskets I'm running and the cylinder head chamber measurements, I'm right at aboit 8.9:1 compression, and with a 230/236 at .050" cam the cold compression numbers seem EXTRA healthy in my opinion. I did not bother to run a compression test with oil in the cylinders since honestly it seemed to me that it cranked awesome for what the build is.

Valve covers were off and I had the wife turning the key for the compression test so I could watch the test gauge and also watch the rockers. To the naked eye, valvetrain appears to be working alright, but really I don't think I'd spot anything unless something was very visibly bad. Lash on all the valves is set equal, and none required more or less adjustment, so that has me hopeful there is no bad lobes on the cam.

Here are my conclusions, and I'd like your opinions on whether you agree or think I should be checking something else...

It would seem to me that with the healthy numbers on the cold compression test, and finally getting cylinder 6 to leak down like the others, that my issue is either ignition related or valvetrain related (like possibly a bent push rod from the holes not being enlarged enough and making contact while it was running, or the contact of the pushrod in the hole hanging it up just enough to not allow the valves to open and close properly). Also thinking it could be a bad valve job or valve seals, since when the car was running the odd bank of cylinders had a lot of smoke out that side of the exhaust. Comparing my cold compression test numbers to what I recall the hot numbers were, it seems maybe because cylinder 4 wasn't firing as evidenced by the white plug, that maybe that's why it was down compared to the other cylinders that were all hot and seemed to be firing. I'm thinking the bottom end is sealing, and so are my head gaskets, and the bad leakdown on cylinder 6 was maybe carbon on the valves or just enough valve opening with the piston not perfectly at TDC to create a leak. Maybe the bottom end can stay together, but yanking the heads at this point to further enlarge the pushrod holes on all of them, as well as checking the valve seals and valve job, is a good idea? Gives me a chance to inspect the cam lobes as well to check if they wore in with lifters properly.

Interested to hear what you guys think. Appreciate the insight and patience reading my short saga here to help me out. Long day, pretty sure I'm not forgetting anything lol