I installed one on a 78 Nova 2dr coupe and I really liked it.  That was a V-8 car and it improved traction from stop and cornering.  Mine was an addco aftermarket piece but mounted the same.

It's certainly an aftermarket part if that is what you are asking Lefty. No original rear bar for a 62-67 X body.

And front bars came only on V8 and wagons, which you likely already know.