Take the piston marked .030 and try to insert it in the other cylinders. Upside down from the top is OK. If it fits all the other holes, go swap those standard-size rings for a .030" oversize set.

It sounds like you are in WAY over your head on this engine rebuild. Is it possible to find a mentor somewhere nearby to assist you with the basic measurements, cleanup, and assembly procedures? Just a few rookie mistakes along the way can torpedo an otherwise simple engine rebuild. Although the guys here are very good at answering questions, we might assume you're doing something we consider to be routine and fail to mention it to you.

Good luck, and keep asking about anything you don't fully understand!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!