Maybe it had a carb option only for vehicles sold in Canada.
I have a Ford truck, older than your Camaro, with a carb. If it was running too rich, first off I"d want to know under what conditions its running rich? If the problem is only at warm idle I visually check the choke plate is fully opening, and if that wasn’t the problem I’d check for any obvious problems in the vacuum and exhaust systems. If still nothing found I’d adjust the idle mixture screws to lean it out. If it wouldn’t run well then, I’d do a compression test … Well, you see the idea … to solve this requires some further investigation at a shop. If you’re bent on replacing something, replace the carburetor. That might work. But then again it might not, so don’t give up your old carb as part of the swap.
One time my truck was running rich and the cause was a screw that holds the choke plate linkage came loose, and this prevented the choke plate from fully opening.