I buy Holley air bleed jets the small ones, takes a 6-32 tap, I drill a bigger hole to just sink the jet, then tap it for the screw in air bleed. I think most of these stock have about .040 idle airbleed, I reduce that to around .030 and it fixes idle quality and the stumble. I got the idea on this forum, do a search, the post had photos.
Also on the stumble, fire up the engine let it idle at normal speed, lossen the plate over the metering rod piston, and slide it to the side, be careful so you don't shoot it out, but play with the throttle and watch the piston move, stretch the spring until the instant you touch the throttle the piston starts to rise, makes them very responsive. They do make different weight springs, I seldom need them unless it has a big cam.
The other issue is the AFB carb design, is a very good one, but it is 50 years old at least, we are not burning the same fuel in our cars that they did 50 years ago. Fuel injection systems adjust for a lot of variables, carb adjust for nothing, if you don't want to drill a few holes and change some parts to get it perfect, just buy and injection system and let the computer do it for you. Tuning a carb is a dying art.