That is quite an improvement in your numbers. The oil sealed up the rings and made a big difference. Remember you are waking up a tired old engine that sat for many years. I know what you mean by all the weird rocker nut adjustment procedures. That applies to engines that have solid lifters or poly-locks. But a stock Pontiac uses a bottle neck stud and a jam nut. The jam nut gets torqued to 20 ft lbs and it 'jams' against the bottle neck. After that once the engine is running the lifters self adjust via the oil pressure and bleed-down hole. When the lifter is on the baseline of the cam the oil pressure fills it through that tiny bleed hole. Once the cam lobe lifts the lifter off, the oil hole is shut off, oil can't be compressed, and the lifter becomes 'solid'. It really is 'set it and forget it' but the jam nut is supposed to be one use only and be replaced every time. I just torque them 5 lbs more each time but that only works a couple of times. Head gaskets are supposed to be one use only. But since the engine was not run, I think you can get away with re-using it. But since everything was cleaned and torqued properly I would not touch it. There is nothing you can do in there without taking the entire engine apart. I would get it running first to give the rings time to loosen up and re-seal. Either you have a tired old engine that needs a complete re-build- or it just needs running time to shake off the cobwebs. I have saved two 400's that were completely filled with water right up to the carburetor. Talk about rusty rings! But they are both running tight and strong now. That is a story for another time but shows you not to toss in the towel just yet. Loosen all the rocker nuts, re-torque them to 20 ft lbs, then spin the engine with the starter and no plugs in. The lifters should self adjust and your valves will open/close properly. Then re-test for compression.