Dude, I started to build a XR75 racer, but it's over my head. I don't have the fabrication skills to make a complete racebike like that. Just getting that XR75 engine I had into a XL70 frame was beyond my skills.
It would've been cool, though. I had a front end from a RD200 that would've been perfect for it.
I race RDs because it already has a good frame.