Rotor size differences

Ok, so I got an extra set of wheels with the 1980 KZ750 LTD that I bought. The guy I bought it from didn't tell me the exact year they came from, but I know they're from another 750 since I also got a head and a few other engine parts.

I mounted my new front tire on the spare rim that I got since the rotors were in better shape than the one that was on the bike. When I tried to mount the rim to the bike, I found out that the rotors are bigger and I can't get the calipers on. I'd rather try and make this rim work instead of having to buy new rotors, but I'm not sure how. Is there another 750 that got upgraded brakes that I could use the calipers from? Any other ideas?

got a picture?

Sorry it took so long, been busy with work

looks like some sort of ltd rotor to me,i didnt realize there was so many differant diameters :S

Thats what confused me. The rim looked identical to the original one, but apparently there's a half inch difference between the two. I think that rim was actually from a standard bike and not and LTD, based on the fender that's on the forks. I thought about using the forks that were with the rim, but the caliper mounting points are the same, so I was guessing the difference was made up in the calipers. I just don't know which calipers to look for.