Suggestions? What screws did you "look for" and what did you "try" with them? How do we (you) know if those were the correct screws and the correct actions or not? We need to be more clear here. 

Later tonight I'll look at a Olivetti-Underwood 21 to see what I can find and somebody else will probably beat me to it.

I don't have a Studio 44 anymore, and the one I had didn't require any alignment (this is the "motion" adjustment you're describing -- getting upper- and lower case letters level on the typing line). But -- and I hope this doesn't sound obnoxious -- are you sure those screws are the right ones? I would look for screws that come into contact with some sort of surface that limits the motion of the segment in the shifted and nonshifted positions. Do those screws you're adjusting seem to control those limit settings? Again, I don't have this machine to inspect, but I would look for adjusting screws on the underside of the machine, rather than on the carriage.