i'm guessing thats not too hard to do...
You might be able to use your original seat pans on the bottom of the GSR seats.
That's basically what I did to get the '89 Si seats in my '90. There was some hardware and stuff that had to swapped over, so that everything would work. I had to transfer the '90 seat back rake aadjuster over to the '89 seat back.
I read somewhere that Honda uses the same basic seat pan in all thier seats. In fact, I may have read that on here about a S2000 seat swap into an EF, or EG. Try searching here, and/or on Honda-tech to find the thread I'm thinking of.