I once read an article by Doug Dutra that said that a properly adjusted valve should feel like dragging the feeler gauge across an oiled kitchen magnet.

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Casually looking for a Clifford hyperpak intake for cheap.

Peanut, canola, or olive? But seriously, that's a very useful description.

I had the leakdown test done today.
cyl 1 30%
cyl 2 40%
cyl 3 30%
cyl 4 22%
cyl 5 35%
cyl 6 40%

The mechanic said he could hear hissing in the exhaust manifold and the carburetor from some of the cylinders.

Oof. Your engine's a worn out pony, time for some rebuild work. A tippy-top perfect engine is below about 12% leakdown without more than 10% variation between best and worst cylinder; above about 20% leakdown you're talking about a tired engine.

If we're hearing hissing in the exhaust and intake, that's pointing at poor valve sealing; you could rework just the cylinder head and that would address valve sealing, but you run the risk of the good-sealing new head finishing off the bottom end (rings, bearings) and then you have to do the rest of the rebuild anyhow. Just because the mech heard hissing in those two places doesn't mean other places are A-OK.

Probably not what you wanted to hear, but good news is this gives you opportunities to make cost-effective improvements (hard valve seats, better camshaft...) and the rebuilt engine will run much better and more efficiently.

If you need to wring some more miles out of an old engine, you can put together an oil catchment with a mason jar and some fittings. Hose from crankcase breather to near bottom of catch jar. Metal scouring pads, pulled apart to loosen the coils, wadded into the jar around the base of that hose. Hose from near top of jar to the air cleaner. Jar capped (find a way to run the hoses thru the lid) and mounted upright. It'll condense the oil out of the crankcase gases so it won't get into the air cleaner and spoil your filter. Periodically you'll have to empty the oil out of the jar.

That's the clean way. The dirty way is to rotate the breather 180°, then run oilproof hose from the breather down over the side of the valve cover, down past the block, so the end dangles down into the slipstream under the car (you don't want it to drag on the street, but you want it to be one of the lowest points under the car). You'll oil down the underside of the car and your car will stink going down the road, but the air filter won't drown.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

aah! just like gm made my old 56 buick! that was a fun car. had factory air!