The RS clutch is perfectly compatible with the NSR.

All you need to do is machine off the outer of an NSR basket, machine out the centre of an NF5 basket and weld the two together. Then you'll need to make up a special pushrod and pusher thingy. An R spec pushrod can be used, just shorten it and machine the radius for the three balls from the NF5 to ride in, and harden and temper it. And then harden and temper the new pusher thingy where the balls ride.

I found that I got the temper wrong on the first one I made as the push rod was still too brittle and cracked, but after reading all about tempering and the temper colours it was fine the second time.

Worked for me. Everything can be made to fit with patience.

Trouble is that this still leaves you with the heavy primary of the NSR, but again, this can be pulled apart and lightened if you so feel the need.