I have quite a few new and old ones that I race with and on the new ones there is a groove on both sides and the lube hole inside seems to
be just a tad to one side. There also is just a little more chamfer to one side, very little. The rod with more material facing the backplate is the way it came new.
I have put them back in both ways and saw no difference in the tach readings. If your going to race with it
everything depends on "HOW" you break it in though. All the ones I broke in are between 16,500 and 16850 on the tach.
Dave