I would be worried that if 1 piston is broke, then the others may go too. If it were mine, and the walls look good, I would look at replacing all the pistons and maybe hit it wil a ball hone and get some new (or newer) pistons and run it. Pistons are fairly cheap nowdays and you can pick the compression you want. Then from there pick a cam and carb and your done......at least with the engine part.