I picked up (likely an overpriced) Univega for my daughter, it's pretty big for her, but it has the "female" sloping down tube. Probably late 80's or early 1990's. It's a project for both of us to work on. I've noticed it's got some really good drop outs (suitable for a fixed gear... likely not anything we're gonna do) that have screws in rear for some manner of adjustment.
Why do they have this, i.e. what purpose do they serve? Merely something to hold it in place? How important are these to be in lining up the rear derailer?