You can relax about the rear windshield Keven; they're all gasketed and all the same size. Even a heated rear window can be installed in the earlier cars that didn't originally come with one. I believe 71 was the first year for the heated rear window (in the US anyway).
The way to tell if the windshield is gasketed or not is to look where the body meets the glass. If you have the body, then trim and then glass, it's a glue in. If it's body, rubber, trim, rubber, glass, then it's gasketed.
The gasket part number, 126.96.36.199.00, appears to be the same for all 105 coupes that used them. The only cars I know for sure that didn't use them are the 72-74 2000 US versions. However, since Sep 1970 is the latest supplement date in my 1750 parts book, 71 US GTVs could also have the glue in (I will check the supp dates before posting, I will check the supp dates...). Can you post a pic?
I agree with italcarguy that the gasketed type is the way to go; much less chance of rust and, from what I've heard, an easier, cleaner leakfree installation.
If you do end up choosing to buy a windshield, make sure it has the "AS-1" designation on it. This ensures that it's US compliant laminated safety glass that won't shatter like the AS-2 side windows do.
Series 2 USA 1750 GTV (in Series 1 European clothing)