I think misunderstanding is where this always goes wrong. People ask if they can "flip" stock manifolds. If "flip" in your mind is up side down, than no. They wont fit. Spark plug holes will be covered. If you mean left on right/ right on left... well- depending on what they came off of, and what they are going into, they may work. There were alot of different configurations of factory manifolds for big blocks. My first use of turbos was with mid 70s New Yorker manifolds. I cut and welded them with ni-rod into the configuration I wanted. Pretty ghetto, but they worked. Plenty of guys would use stock manifolds in stock locations, make a pipe from one to the other, and weld a flange directly onto one of the manifolds for the turbo.In the 70s/80s Turbosonic made a 440 manifold with the flange cast into it that made its way onto many Winnebago motor homes.
If you don't have a modified chassis car, stock stuff will take you far beyond what the car will hold. Spend money on your fuel and ignition. EFI covers both bases at once. Carb can be expensive and will never get you to where you can be with efi. Price both and you will find efi is not much more if you aren't afraid to do a little hunting.