Recently had to rebuild the top-end of my QT50. It had the 60cc cylinder/head on it but the oil pump went out and subsequently trashed my cylinder & piston. Cylinder is beyond boring according to the machine shop; but the head is good. $25 including shipping.
I also have an extra piston bearing & circlips in good shape. Bearing P/N 93310-210M0-00. $10 incl shipping