If you don't have quality tools to measure the bore for out of round Dons advice is fine, but there is no substitution for doing the job correctly with the proper tools. A quality hone can fix a bore and if you are patient enough, hone it up one size. But that only applies if you are using a positive pressure hone such as a Sunnan. If your hone is a spring loaded unit that you got from the local auto parts or Harbour Freight it has NO use whatsoever in building a racing motor, throw it away. There is no way to build a quality racing motor without starting with a quality bore, not trying to discourage you from building your own motor but if you don't know the answer to these questions you are better off sending the motor out for a quality hone or bore job. Either buy the new piston from the shop doing the work or if you already have a piston send it with the block. Suggest you send it out to a kart engine builder, as they would already have a set up to get it done properly, a local machine shop probably needs to spend so much time on set up that it would be too expensive.