Your model #3012 is years 1952 – 1954. The exact year is determined by serial number I believe. Someone has that information here on the site. The original part #203152 is for each ring. Supercedes to #378412 for a set of standard rings per piston. MarineEngine.com has them, but $75 per set is pretty high.
I have some I bought, but they are in raw form. That means you have to set the end gap & cut the clearance for the alignment pin in the piston. They are just straight cut at the end now. Let me see how many sets I have?
Sets of rings are usually on eBay all the time, but none as of tonight.
PM me & lets see if I can help you out. If you aren’t comfortable with raw rings, somebody in the club has to have some left over. Put an ad in "Free Classifieds – Wanted to Buy"? Tomahawk is coming up?
Dan in TN