Before you make a piston decision you should measure the bore taper. If it is out 0.003" you should consider boring and honeing to next size up, and yes then buy all new pistons. If it is 0.004" taper, then you almost have to go up a size. You'll need to borrow, or rent a bore gauge. If you have it torn down this far, no excuse not to do a good job. The piece missing off the skirt would cause me to go up a size. How many hours on the engine?