Same year and model as mine.
Do yourself a favour and keep it...them 4 stroke pure dirt bikes are junk.
Curious what happened that you had to rebuild the top end at just 20 hours?
Maybe borrow a pals four stroker for a few hours of riding, and then decide.
Also they constantly need valves set, and top end overhauls are frequent items and very expensive and time consuming compared to a 2 stroke.
But mostly they are gutless wonders.
I race mine and i can beat all the 450's no problem.