Awsome project! I had an XR250 in '96, and I loved it. Half of the fun is the simplicity. I raced it a bit (this was before the current crop of higher performance four strokes) and beat a lot of bigger, "faster" bikes, gettign top three finishes in the four stroke B class. People don't like getting passed by a little trail bike.
Definitely get the suspension properly set up. I found out the stupid way that these bikes can go a lot faster than the suspension will tolerate. And watch your toes! Ten inches of travel leaves them in harm's way quite often.