What kind, exactly, intended for what kind of motor? This is a carburetor-shaped can of worms. Good Slant-6 carburetors are harder to get than they used to be, but they're not impossible yet; you may wind up finding it easiest and best to go back to a more application-appropriate carb of one kind or another.
Does this car have the rotating-rod throttle control common to all pre-'67 Slant-6 A-bodies except '65-'66 with factory A/C? Or a cable-type setup?