1) Get in touch with @teazerTechnically I didn't purchase it because it was free, but I now have this RD250 race bike. Hasn't been run since the 90s, but the engine has been rebuilt within the past few years. I'm getting a solid 120 psi from both cylinders when kicking it over (cold). It has vintage shouldered Borrani rims, and not much else. Looks like it was set up to run premix. Previous owner/builder was a mechanical engineering instructor at Oregon State University.
2) source top end parts, lots of them
3) buy stock in your favorite spark plug company
4) source and rebuild crankshafts
5) read http://www.amrca.com/tech/tuners.pdf
6) read it again
7) watch one of your children's first year college tuition evaporate in a blue haze of Castrol R
You may never have as much fun setting fire to to several $k...