I should clarify that my trans didn't have this style of detent at all. They were all the round kind. The shift rail kit came with 2 of these hatchet ones. On the David Kee website they describe the shift rail kit as '65. And my shop manual is a '67. My trans is a '67 also but it differs from the picture in that mine doesn't have a set screw holding the 1-2 detent spring in.
Thanks, Chuck