I did it with '91 (non USD) forks and it is easy. They slot right in but you need to set them 5mm recessed into the top triple clamp and it gives you an aggressive rake angle. I used the RS250 calipers and disks as well. Not sure how easy it would be to mount the NSR brakes on the RS250 nforks.
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MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-