If you look at Suzuki's steering head bearing part list, you will be amazed. They have only made a handful to cover all different models. Most of the GS, GSF, and GSXR stuff will interchange. It is best to buy everything together, forks, bars, wheel, rotors, calipers ect as some of the individual pieces will not interchange. But as far as bolting everything on, it is a snap.
The very late model GSXR stuff is very short and could present ground clearance problems. The mid 90's stuff is probably best as far as this goes. You will run into problems with fork stops and steering lock.
I recently put a 1993 Katana 750 front end- 41mm tubes, floating discs, 17in front- on my 1983 GS750ED. My goal was running modern 17in rubber with improved brakes. Everything bolted right up, I did have to fabricate fork stops and cut out the steering lock. Also, fabricate instrument carrier and riser clipons as these tubes were 1.5in shorter than stock.
Anyway, it is a very popular mod on the old GS bikes and can be done. Ride On, Ed
2005 GSF1200SZ
1983 GS750ED