Along with the said engine mods, worth fitting new piston rings or even fresh complete top end. Its not so expensive and will give you a good platform for track use.

Definitely work on the suspension, it was only after riding my 21 track bike & RS250 race bike back to back, I realised how tired the NSR suspension is. Serious dull handling.

Also, get rid of as much weight as possible, even the road wiring loom is pretty heavy. Ditch all unrequired electrics including speedo. HRC race looms occasionally come up on Yahoo Auctions, sometimes for low prices. Or you can convert your road loom, or buy a spare road loom and hack it!

Ditching the oil injector is another good way to shave off weight, go to premix with a ratio of no less oil than 30:1.

If you become a member, you can get your bike in the member build section Also gives you access to the HRC section, useful when looking for HRC race parts on Yahoo auctions and wondering what their value is / what difference they make etc.

This link to the garage shows what I did to my MC21 track bike

http://www.nsr250.net/forums/garage.php?mode=view_vehicle&CID=95

Good luck.
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30