Are you sure you were on TDC compression on all the cylinders during the leakdown test? The pistons come to the top twice in a 4-stroke cycle, once on "overlap" between the exhaust and intake strokes with both valves slightly open, and again one turn of the crankshaft later with both valves closed.

Watch the valves on a cylinder as you rotate the engine, and when you see the exhaust closing and the intake beginning to open, go halfway around the firing order and pressurize that cylinder. For instance: #1 valves moving/pressurize #6. Listen for air leaks at the carburetor, tailpipe, and oil filler to determine what's leaking- - - -intake or exhaust valves or piston rings. Bubbles in the radiator will indicate a cracked block or head, or blown head gasket.

Continue around the firing order until all cylinders have been inspected. I suspect you've got some sticky valve guides that are preventing the valves from closing fully. Did you loosen the valve adjustment slightly before beginning the leakdown test, and did you tap the valve ends of the rocker arms several times with a dead blow hammer while squirting penetrating oil on the valve stems? I do that every time I try to resurrect an engine from long term storage.
Jerry

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