www.edmunds.com is a good place to research the differences in standard features and options. But I'll try to do a brief summary of the stuff you asked about. You seem to know most of this stuff but 98 was the changeover.

94-95 - Have OBD-1 emissions electronics which supposedly makes performance mods more effective than with newer models.
96 - OBD-2 introduced.
98 - Headlights and taillights changed as did front and rear bumpers. Most people like the newer look.
99-01 - GS-Rs come with leather standard.

And yes, pre-98 and 98+ taillights are interchangeable.