I know it can be done on the 09+ bikes with just a rotor and bracket. I'm curious if the ebc kit works on the first generation

 

As said, the 300 mm rotor that is used on the KLX650C and the KLX250SF is a bolt on with the right bracket. One way to learn what works is to see what the bracket part number is on the 09 for both the S and SF, then compare to the brackets on the earlier models If the S brackets match that would mean the SF should work on the earlier bike. If not, it might be possible to use the fork leg from a 650C on the earlier bike.

Easiest and least expensive would be a stainless line and some softer high grip pads.