You can see the thin scribe on the right side . . We have this case marked out to remove material to clear the crank pin for stroker flywheels. This stroke is greater, so the pinion(and nut) is moved up, and if we don't remove material from these bosses, it will hit the case. Depending on the size of the stroke, you must remove material from other areas of the cases too. S&S has excellent instructions on how to do these modifications correctly.