The 1-piece rings work better in this small bore, high-RPM engine. I have not seen 3-piece rings for this one.
When installing them, I first break the inside edge of the oil ring at the open ends, as they often have a slight burr right there. If you're worried about scratching the piston lands (which is only an Internet problem, not a real one...) on the way down, slip a thin sheet of brass or a feeler gage alongside the piston and let the ring slide down over it, instead.