I'm not really sure what the RS means. I got these cranks with a sprint car block. Sometimes Mopar did weird part number etc for race teams. These have a 8 and 6 bolt pattern too. I already sold one of the two. The one I have left doesn't have a part number on it just a 3.580 stroke. There identical cranks, 340 mains 2.500 and 2.100 rods