I measure the R pair with a Dial caliper and they are .010" shorter than my other SP pair. Maybe the previous owners of both motors put wrong set of barrels. Hey at least they were matching set meaning same height barrels. As for the heads, who knows. Can you tell which one is for what base on the numbers at the top of the heads? Also HRC Part #s- What is meant by 06122-kv3-680 or 830. What does the last 3 digit represent?