After an engine swap for a 79 20R, my 1980 pickup started stalling once it dropped to low idle. I noticed through the sighting glass that the float level was low, though within the limits. I tried to readjust it bending the tab according to spec, and that made it worse, no low idle at all, though I could get it to idle using my hand as a choke, pointing to a lean condition. But each attempt to change it is a bigger pain in the butt than the last, with lots of tiny parts to drop and never find again. Can anyone tell me if I'm on the right track here? It did idle some up unitil I did the the readjustment, which tells my I bent in the wrong direction, meaning up not down, whatever the spec said.

 

Considering it did idle some before you changed the float tab position, I'd say it might be more of a matter of a vacuum leak causing a lean condition. On high idle (cold start, choke closed) a vacuum leak doesn't make as much difference, as the engine is pulling more fuel & air than at hot "regular" idle speed. Hot idle doesn't require as much fuel & air, so any extra air introduced via a vacuum leak would result in a lean condition.
What I would do -
Check for missing, cracked, disconnected or loose vacuum hoses; replace with new ones where needed. Use some quality vacuum caps (the rubber ones, NOT the plastic ones) to cap off any vacuum ports that aren't being used. Reset the float tab position to original spec to make sure you aren't flooding or starving the float bowl, & have proper fuel level. Inspect the carb cover gasket when I have the cover off to do the float tab, making sure it is intact & not causing a vacuum leak at the gasket.

You didn't say if this is an older carb or not, rebuilt or not. If it's an older intact carb with a fair amount of miles on it, it's possible to have a vacuum leak at the throttle shaft bushings in the base of the carb. To check for this shoot some carb cleaner at each bushing while the engine is running. If the bushings are loose & causing a vacuum leak, you should hear the engine speed up right after you spray the carb cleaner at them. The cleaner will be getting past the loose bushing(s) & acting like extra fuel, correcting the lean condition very temporarily. But it would confirm leaky bushings.
The only fix for that is a completely rebuilt carb. My '78 had this problem. My solution was to trade my old carb for a another one completely rebuilt, including throttle shaft bushings, from National Carb. Reference link here: https://nationalcarburetors.com/Toyo...-CC_p_520.html
There is no way to replace the bushings yourself, as they are not available for retail purchase anywhere that I could find.

You could also go to a Weber 32/36 as a replacement, but that would cost about $200 more, for the carb & adapter kit. Reference: https://www.yotashop.com/weber-carbu...75-1991-k746m/

So, do what I've described so you can get a better diagnosis, then you can decide what direction you want to go. Me personally I like the stock 20R carb & it does what I need it to do. I've been running the rebuilt one for over 6 years now with no problems.