I agree with what others above have said, if the rings were all lined up and valve were right I would be worried if below #70's of compression same with rings good and valves tight. That's a lot of air to escape out some very small holes in a
very short time, I would still think at least #50's even with a huge overlap cam. The only time I have seen "zero" (10/20#'s) was with a single cyl. Briggs with both valves frozen [rusted] open "Full lift" [sub 0.300"] less than full lift will not turn over because the valves are stopping it from turning. I will, leave out the "Fully Ventilated Piston" scenario's. If by "Zero" you mean very little feel of compression you may have not prefilled your lifters as you may have thought you did [some don't fill as easily as others dependant on oil viscosity and oil hole placement in the can of oil] this would make any and all preload hold the valves open. Did you try a leak down test? You can also do this with out a gauge you will just use the adapter to hold air in the cylinder*. Then listen to intake then exhaust then crankcase breather and finally radiator, you are listening for escaping air, then add oil to the cyl. roll over the engine and repeat. This will allow you to help determine the source of the problem, valves [intake and exhaust] should be ZERO leakage as should the rad, breather will always have some but should be minimal on a fresh build [slightly less after the rings seat]. I would think that you will find a combination of valve timing and valve lash as your issue, this based on my early "Learning Opportunities" I never make mistakes!
Now onto weather to pull and disassemble and reassemble that will be first determined by the answer to this question, RED antifreeze, Start immediately Red [orange & Pink too] will attack your brand new Main, Rod, and cam bearings, minutes count! Clean them fully with a mild solvent Kerosene, Paint Thinners, Diesel (good choice), lacquer thinner would be my last choice but I don't know of any issues with lacquer and bearings then a final with alcohol. Green go through all of the other checks first and then reassess. Please Keep us informed. Harry *For air in the cyl. tests:
https://www.autozone.com/test-scan-and- ... 750866_0_0
I'm not a hoarder I'm a preservationist 78 Monza Spyder (~Soon(ish +/- I guess) To Be 2+2 with Spoilers)