The small screws are there to limit the amount of turns the idle screws can be turned out.
The mixture screws have a waist on them, think 36 24 36 and the small screw intersects the mixture screw at the 24 part.
View attachment 1715761810
[Found!] - Carter Idle Adjuster Screw (for CAP Carb)
It was a CAP thing to prevent tampering by the owner.
As for welding I think the thought there is weld a rod to the broken part in the carb and use it to unscrew the broken bit.
This is from the 4bbl but you can see the set screw sticking out. I was able to drill out a lead plug ( lower hole) to get the broken part out.
View attachment 1715761798
