How it works is the fenders are pretty much interchangable, but you have to use the proper year seat pan for the same year fenders. I've even seen people use the 83, 84, 85 tank and fenders on the earlier frames. Oh, and it helps to use the proper rubber pad as well, the one that goes under gas tank rear tab.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90