Working on motor

Before you take the rings out, use a feeler gauge and measure the ring side clearance; you do this by seeing how thick a feeler gauge can be slipped between a ring and it's groove. There is a spec on this; with old rings it ought to not be too much above the maximum; ti wil tighten up with new rings. The purpose is to see if the ring grooves are worn; if they are then new rings won't last that long.

New rings for sure. If I understand your question about what to buy, then plain cast iron will do but moly top ring sets will tend to break in faster/more easily.

You do know that you should hone the cylinders before installing the new rings?