A. How does it shoot / feed? Not broke? Don't fix it.
B. Provided the gun takes a standard slide stop measure from the slide stop pin hole to the plunger tip between frames to get a perhaps relevant read on where things are at...
C you say assemble with a punch? I assume you mean get the slide stop back in? You can swap plungers for under 10 bucks of what is really slick is to take a triangular file and cut a little v in the back of the slide stop to allow it to get started depressing the plunger in when you reassemble. Thread in gunsmithing section at 1911 forum has explanation and pics.
D. STI is a good gun.. Perhaps tighter than some this is not a bad thing!