They cut that hole in this board larger and square and used that odd clip instead of a nut, all to vent some heat out of the gauge with limiter inside. By 1967 they figured out this wasn't necessary. The 67 board has round hole, same speedy nut on the stud, and bakelite cap over the stud and nut. Cap looks much like a household wire nut.
You could have tossed the clip and put a 10-32 nut on the stud.
