There is not a great solution for retaining the plastics of the 93 body and melding it with the upper fairing of an 88-89 body.
The thing is, The GSXR changed from 89 to 90 and again from 92 to 93. Of those, the most drastic was the 92 to 93. The frame changed, the engines got water cooling and the body changed from a 5 piece front body to a 3 piece front body.
The head light was mostly the same from 90 to 95. The “capsule” type headlight required more stand off from the steering head tube to fit. The 88-89 head light bucket is flatter and required less clearance.
Suzuki simply made a couple of aluminum brackets that bolt to the steering head tube and the upper fairing stay to create the additional room. Hence, bolting an 88-89 upper stay on a 90-92 frame is plug & play. Even the electrical uses the same connectors etc.
While I’ve worked on a 93, I didn’t do anything extensive enough to comment on whether Suzuki went the same route with regards to the stay-steer tube arrangement or if it is all completely different. I recall it being different but how much so I no longer remember.
If you can sort the stand off issue out, you may be able to just trim the fiber glass upper to mate to the lower seamlessly. The major difference is the 88-89 upper extends down and fairly far back to the at least the front of the valve cover. The 93 plastics have a curved 90 degree-ish cut out that is filled with the side plastics.
You can see what I mean on the pic above. The lower edge of the upper is relatively straight and extends down and back towards the tank.
Compare that to the side plastic of a 93-95 below. Evident from the shape that they will not mate up at their respective edges. However, there is enough room on the 88-89 upper to trim down to mate to the 93-95 sides.
Not saying you won’t have to fab a filler panel or 2 to make the join look seamless but it’s the best solution I can come up with for you.
