CALLING ENGINE GUYS/GALS

You can do a leakdown test a number of ways and get different results. When you get a low number, you have to take a step back and think about the why of it.
Most testers will ask for a very low regulated pressure; I have seen as low as 30psi. That is IMO, nonsense. The idling cylinder pressure will be many times that, and at WOT the pressure will rise to perhaps 800psi or more, so why would the tester manufacturer specify such a low test pressure? IDK, but I've never tested at less than 80psi.

An engine sitting for years will have little to no oil on the cylinder walls. IMO, where your test would fail would be from lack of oil on the cylinder walls and lack of oil in the ring lands, which provides the major sealing.
This is the same reason why a gas-flooded engine is hard to restart; all the oil has been flushed into the oilpan, and there is very little cranking cylinder pressure being produced. Simply pulling the plugs and cleaning the gas out, then injecting some oil, then cranking it to distribute that just-injected oil onto/into the ringlands, then blowing out the excess, then re-installing the cleaned plugs, almost without exception will get it running again. Without oil sealing the rings to BOTH the cylinder walls AND the lands, the pressure HAS to be low; it cannot be otherwise.
Additionally; at rest, no matter where the engine stops, there will never be more than two to perhaps four valves that are on the seat. When an engine sits for long periods of time all those open valves are gonna grow hair, and it takes fire to burn it off. Or mechanical help. As long as that fuzz is on there, the valve will Not seal. and this is excuse #2 for a low LD test results.
You had the right idea in removing the valve gear, but you didn't follow it thru, or at least you didn't mention doing so.
Doing a LD test at 80psi or more, with the valve gear off, will blow the piston to the bottom. Read your tester. Then tap each of the valve stem pairs of the cylinder being so tested several times with a small hammer, to pop them off the seats. When the valve slams back onto the seat, it will crush the oxidation, then the next tap will allow the 80psi to blow the rust out. After a few taps, of each pair, the pitch of the sound will change as the valves begins to seal again. Pop the pair a few more times to burn the sound into your brain, then move to another pair. Then repeat the LD test. Finally inject some oil into all the cylinders and starter crank her, with the plugs out, to lube the rings and blow out the excess.
Now you can do a proper LD test. And you can see the progression in the results as the cylinder begins to seal.
However, the least worn part of the cylinder is at the bottom, and you will get the best results down there, which, with ball-honed or stone-deglazed cylinders, may not be accurate. So it behooves you to do a final LD test, with the piston at TDC.
However, at 80psi this is/can be dangerous. If you just dump 80 in there all at one time, the piston is not likely gonna stay at the top, and it's gonna take a very long bar to keep it there. On a 3.91 bore, 80 psi is a force of 960 pounds. If the piston moves, and you get caught off-guard it can flip that bar hard over in the blink of an eye, with plenty of force to break bones.
To prevent that, I installed a ball-valve and a restriction in the air line. With this I can control the amount of air entering the cylinder without changing the regulator setting, and therefore have lots of time to reposition the bar to keep the piston at exactly TDC, even as the chamber is filling.
At the top of the bore, on a previously used engine, the worn area is neither round nor straight nor perpendicular to the axis of the cylinder. So the LD test is gonna give you another set of numbers. Eighty psi will blow some of the sealing oil down, but the number you finally get, will be representative, so live with it, or bore it.

BTW-1
In Smokey Yunich's book, Power Secrets, he says that if he had an engine with over 4% LD, he didn't have a race engine anymore. I can tell you that at 2%, I have had incredible results. Results that FABO members flat-out deny are possible. In this case I don't mind being insinuated or even directly called, a liar.
BTW-2
In addition to my Hotrod 367;
I have a dingle-balled and re-ringed original-bore/original pistons, 1973 Smoggerteen, that is still great fun to drive. with 3.55s, a 904, headers/dual exhaust/ and an old TQ on a small-port intake. Ima guessing it is pushing 250,000 and more miles on the short (but not the rings). I have had this engine since the mid-70s.
BTW-3
It's just too bad that the heads are already off.
If it was mine; I would clean it up and install new gaskets, but tighten to only 80% of spec, (which IIRC is 95ftlbs). I would repeat the LD test as described above, to see what you really have. If the engine is not heat-cycled, the gaskets should be fine; I know the FelPro .039s would be.
BTW-4
it is possible to assemble a freshly bored engine, and check the leakdown before installing it, and get a really really small number. I wouldn't install my engine any other way.

EDIT
I do not mean to imply that you need less than 4% to have a decent driver. I'm just saying that it is possible to get to less than 4%. I''ll bet there are plenty of driver's out there at 10% LD. The think is this; on a GOOD day, a good low-mileage 318 might make
135psi CCP at sealevel at 4% leakage. Which means, That at zero LD, the pressure would be ;
135/96%= 140psi.. If you had one at 10%leakage, that would then be
140 x 90%= 126psi
So then from 135 to 126 may not seem like much difference, but giving the Wallace calculator a workout, I see that at 8/1 Scr and 900ft elevation, that amounts to a V/P index of 114.
At 126psi, the V/P is equivalent to what you would get at 2700st elevation with still 8/1 Scr, or
a drop in Scr to 7.5, which at 900ft equates to a V/P of just 106 .
106/114 equates to a V/P loss of 7%, and so a loss of performance of that same 7%, at WOT beginning at stall rpm, and diminishing with rpm to break even somewhere north of 3000 rpm with the stock cam.
This translates at part throttle to always having to press the gas pedal harder than what would be possible with a higher VP. And of course that also sucks gas mileage.
All in all, low cylinder pressure is a bad thing. As is large Leakage.
Large leakage also means combustion pressure is gonna blow into the pan. When the engine cools of, water that came in thru the carb as humidity will now condense in the pan, forming acids with the blow-by, that are then gonna be in the oil, ready to be pumped all thru your engine on the next warm-up cycle, where they attack anything not made of iron or steel or rubber. Not to mention that the PCV is sucking it all up as it turns to vapor.
And almost finally, most of this scenario happens in the first inch of ring-travel.
And finally; in that last inch, the ring gap shrinks and grows by 3.1416 times the change in bore size. So if your bore at 1" down is 3.910 and at the very top just under the ridge is 3.917, that is .007 , and so the gaps are changing .022! and while they are doing that, they are scrubbing the ring-lands, wearing both the rings and the pistons.
So no, you do not have to target 2% or even 4% Leakdown, but you can clearly see the problems at 210% which, intuitively, does not seem like much. But from the engine's point of view is huge.


Read about VP here; V/P Index Calculation