Going to suggest here that the Z-Bars and their attendant linkage are generational to the year/model groups that they fit. By this I mean that the G series of vehicles, MonteCarlo, El Camino, Malibu, Cutlass, Regal, Grand Prix and Grand Am all used the same basic chassis assembly. That tends to mean that all the required holes for the various brackets should be present even though they may not be used for a specific application.
For the earlier A designated predecessors, all this would be different as their parts are mostly exclusive to them.
Chronologically, the A's were produced up until 1977. In 1978, everything shrank, and the mid line became the G-series. They technically ceased production in 1987. If you hear of or see a G that is being depicted as an 88, it is an 87 leftover that was redated for sale the following year.