funny you ask that because I am slightly miffed at novarossi's current lettering system, I thought the R was a rotary carb version but I could be wrong. However I think I can saftly say that if it is an NS version it has the billet piston. I used to have a very good handle on it all but its gettin a little fuzzy now that i'm not into new customer motors every day.

Oddly enouth the NS's we get here are marked
NS12S3-A1