Pumping compressed air into the cylinders without a leakdown tester is ABSOLUTELY FINE for testing valves, head gaskets, and looking for cracked castings. Because the only acceptable result is ZERO leakage past the valves, into an adjoining cylinder, or into the cooling system.
Evaluating leakage past the rings requires gauges to measure the leakage. There will always be "some" leakage past the rings. The crankcase/lifter valley/valve covers are gigantic echo-chambers, small leaks can "sound" like big leaks, big leaks may--or may not--sound all that huge.
I would NOT loosen or remove the rockers--at least at first. If you have no leakage past the valves, you're set. Assess the leakage past the rings, into the cooling system and adjacent cylinders, and move on. If you do have leakage past the valve(s), then you can loosen the rocker(s) on that cylinder, which may or may not confirm that the lifter preload was set too tight.
If you loosen the rockers first, you'll never know that the lifter preload was/wasn't correct.
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