What do I measure to determine whether my coupler is the "short" or "long" style?

I have seen a few of these clips in the swap meets (usually in a pile of other assorted junk) but I don't know how to tell if it will fit my car.

(70 B-body with PS if that matters)


1969 Dodge Coronet Super Bee 383 A4
1970 Plymouth Road Runner 440 FC7 (sold)