Nitrous for '99 900RR

Which is the best kit for a '99 900RR?  Also do I have inject the nitrous directly into the carbs or can I inject it in the airbox?

any 4 cylindar EFI kit will do. I would go wet to compensate for what your computer wont. You can fog it but make sure the N2O is not going to pool anywhere.

'99 CBR's aren't EFI.  They are carburated.  Will this still work?

You'll have to go with a wet kit if you're caburated. You should tap the intake boots after the carbs. I wouldn't do into into the airbox with a wet kit.