Actually, the entire line of XR600 plastics will swap over. My 85 XR600 is done up with 2000 model seat, tank, and side covers. The ONLY difference was the seat bolts. One side was about an inch forward than the original. I made a small aluminum plate to make up the difference.
I can say that you will need to get all of the body as the parts don't swap out any other way. By the way, the only difference in the airbox is the carb boots. The side cover fits perfect with no problem or wrestling with it.