SteeleRubber Gaskets & Windshields

I'm planning to replace the front windshield glass in my '71 Dart GT (45+ years of road rage has taken its toll). My mechanic/buddy said I might as well replace the back glass gasket at the same time. While perusing SteeleRubber's website I found 1 gasket for the front windshield and 2 gaskets for the rear glass. Apparently vinyl top cars use a different rear gasket than non-vinyl top cars. Who'd of thought? Is there a big difference between the 2? So why isn't there 2 gaskets for the front windshield? Eventually I'd like to remove the vinyl top, but that may be several years away. Would I need to replace the rear gasket again once the vinyl top is removed?

With all that said, who/where has the best replacement windshield? I don't care if its tinted or clear.