Mine was a 326 2bbl and had single exhaust. I know it had single exhaust because there's a backing plate on the hanger mount behind the rear seats on one side only. This is a testament to how custom built our birds are. You'd think they would have backing plates on both sides just in case it would get dual exhaust down the assembly line. I cursed GM for not spending the extra dollar to put on both backing plates since there is no way to reach the back side. I ended up just screwing into the sheet metal which appears to be surviving.