If its the OEM carb, it is already optimally jetted, tuned, set up, etc. for your engine. Unless the casting or other parts are worn or damaged beyond repair, you will likely find no better carburetor for you car. Even a full on restoration (you likely only need a good rebuild) would be cheaper and less hassle than going to an after market unit. Once you get the after market carb, you will likely need to re-jet and otherwise modify to be right for your application AND it will no longer be original.
HTH,
Gene