Help with 1920 Holley carb

The screw in your last photo is for adjusting the fast idle speed.

Service manual will you help alot.
MyMopar - Mopar Forums & Information - Service Manuals
Originals are available used and reprints are sold by various companies. Bishko is one.

A lot of very good information is in Master Technician Service Conference - Chrysler's Training for Mechanics
1966 222 and 1970 273 are two on how carburetors work.

Others get into specific mechanical adjsutments.
If some of the info is complicated then come back to it.

The 1969 master techs are also in The 1970 Hamtramck Registry Library Page (1965 - 1969)
which has lots of factory and dealer info. Some of which you and your son may also find interesting.