1968 340 AVS 4425S carb problems

Sounds like progress.
Doesn't take much to clog up a idle circuit. Well alot compared fuel injector. LOL

Careful not to put too much emphasis on the vacuum reading, especially in neutral.
At a given rpm and conditions, yes higher vacuum indicates stronger.
The condition in gear is much higher load than in neutral.
The engine needs a richer mixture under high load. At idle the engine makes little power so slipping it into first (or Drive) is a relatively high load.

A typical idle mix procedure without a CO tester was to lean the mix just to the point rpm was about to drop. Then make it a little richer.

As you know, for early CAP and CAS, they purposely ran the idle mix leaner than ideal. To make up for that, the idle rpms were increased a little.