Actually I think it's more accurate to say that rear sway bars were available for the Formal police package cars, but actually are quite rare.
Because of the Torsion bar suspension, and the fact that Mopars handled better than their counterparts, Chrysler Corporation was pretty slow to the rear sway bar game.
Most C bodies did not come equipped with a rear sway bar...even the cop cars. Quite rare on a Formal. Although I have seen them on Formals in the wreckers, and only on police cars, and only a couple of times, I cannot even recall the exact year of the cars...could be that it was an offering towards the end (77 only or something).
The waters become more muddy if you try and consult the factory documentation.
None of my FSMs indicate it was available for C bodies...so maybe its only something that was only police order?
The cars that I saw in the wrecking yard (back in the 80s) both looked like they were constructed with the rear bars and that they were not add ons.
I don't think a sway bar was available for a C body from the factory pre-74. Never seen it in decades of C body ownership and scrap yarding. It does not appear in any of the dealer books or FSMs I have.
Anyways, the C body sway bars I saw were both like what you see below, half brackets that could be added/ stacked onto the iso clamp (note the large hole). Same style as the early B body rear sway bar offering.