Dood, it is a factory set up, but if you're still running a Y pipe and a cat should bolt on for cheap $$$
Stock Olds dual system
The only thing factory on that exhaust MIGHT be the downpipe from the passenger side exh manifold to the cat converter. The rest of the system isn't factory equipment. Still would work, though. And if you need one and can't find any...
The main real difference is the 79 used the old style converter and the newer style uses an air injection for the 2nd bed in the cat to drive down hydrocarbons and carbon monoxide. So unless you install an AIR system on the 79, the cat will still work, just not as well as if it had air injection.
It's a 6 of one half dozen of the other type of setup. The original 79 "dual" outlets end up pretty much the same as the other dual outlet versions. One just splits sooner than the other and I don't think one flows any better than the other. Just my hunch.