Tews, I'm with you on the gsxr front end. I think performance-wise it's the way to go; but, the esthetics are not quite correct for these bikes. I was contemplating going the gsxr route for my '78 550. It was a close decision for me. Instead, I decided on RaceTech in the stock tubes, tappered bearings, a brace and dual discs. Personally, I like the "look" much better and it compliments the rest of the bike. After raining on your parade, I do really like what you have done.
The 77 & 78 rear hubs are indeed different from earlier models and require different spacers. I used a 76 hub on my 78 frame and had a few spacer fitment issues - all good now.