Old school, woods, 2 stroke, light, street legal, 15 to 30 hp...wow, not a lot of options...77-78 DT175 fits just about everything in your list. 216 lb no fuel, 18 hp, street legal, old school, monoshock...yup fits them all. I really miss mine as it was easy to ride (though small, I am 5' 8", 170 lbs and I could man handle it easy), and truely could hit 80 mph (as long as you had no head wind). The later DT175's were softer sprung and a little more playbike, the earlier ones were twin shock.
I hate to say this in the 2 stroke section, but the 91-96 XR250L would be the best option for you. Better gass mileage, higher speed, taller, better suspension and disc brakes. Power is equal, but the DT seems better in that department. Basically a street legal XR, where the XL's were not quite up to snuff suspension wise.
KDX200 would be the ticket if you didn't need street legal.