The IPL's that I have show different part numbers, 83334 for the 10-10S and 87680 for the Pro 10-10, MAC 10-10, and MAC 10-10A.
Different part numbers doesn't always mean different different parts with McCulloch, you may have to find someone with a reference list that can cross those part numbers. The older 10 Series service manual shows two different springs that can be used interchangeably but does not reference the part numbers, however I know from experience that the original was 68626 used in all of the RH start saws.
Todd, are you sure the RH start springs won't work in the LH start saws?
Mark