The ad said everything is custom. I see the custom stock shocks, custom stock a arms, custom stock plastic, custom stock swingarm. All the removed stock parts is custom. That's a deal!
if its a 76 or 77mm piston then it sounds like it a Trinity Racing 256 cylinder on its last bore with a stroker crank.
Trinity Racing did make some 300cc size bb stroker kits back in the day!