I went thru 4 Holley 1920 rebuild carbs from auto parts over decades before I got one that would idle smooth. I expect the metering block in all the others was clogged. They don't rebuild that and it isn't normally opened. Some guys here know how to blow them out w/ compressed air without taking the carb apart. You blow thru some of the holes on the underside. When clogged, the engine idles lean, which is why even all the way out you never find an optimum adjustment. To verify, close the choke slightly (richens) and if it runs better it was on the lean side. In general, too-lean makes it shake and too-rich makes it slow down but still run smooth, eventually pouring black smoke out the tailpipe and eventually die.
When lean, it will slow way down in going from N to D and stutter as you drive away from a stop sign. You will find that it wants much more spark advance at idle. Indeed, it gets into a positive feedback mode in P or N at the normal ~5 deg advance setting since as the engine speeds up it gets more advance, speeds up more, etc.
I never tried the later Holley 1945. I have a Carter BBS on my 1964 slant and it idles unbelievably smooth. When I first drove it home, I even actuated the starter once on the side of the highway, thinking the engine wasn't running (had died from "no charging", funky wiring). The small factory air cleaner helps keep it quiet. You can't even see the engine moving at idle, whereas my 1969 slant used to shake until I got the good 1920. The only smoother engine I have seen is a neighbor's 1950's Buick straight-8. You wouldn't believe his engine is idling if you didn't see the pulleys turning.