I agree with the recommendation to use an original Ford Holley. Not that an aftermarket unit can’t be made to function just fine, but as others have pointed out, they just don’t have the right look. The original 600 cfm units are pretty widely available and it shouldn’t be difficult to find a reasonably priced example. They work well, and if the car is otherwise all stock, that’s what I’d go with. As Mike mentioned, the 735 CJ Holley is externally almost identical, and is a good choice for a stealthly performance boost. The old Ford “Muscle Parts” handbook recommended this very change. Getting full benefit, however, requires additional modifications, such as headers or CJ exhaust manifolds, and the CJ or an aluminum high-flow intake. Unless you find a super bargain on a CJ carb, the gains to be had on an otherwise stock 390 don’t justify the additional expense, in my mind.
In either case, restoring a neglected Holley to fully functional status isn’t particularly difficult, it just requires some time and attention to detail. Always use genuine Holley parts, and remember that cleanliness is critical.
The chemicals and supplies necessary for appearance restoration are more of an investment than is practical for the typical hobbyist. If that’s important, someone like Drew at Air Fuel Spark can restore both the function and appearance to like new.
Sounds like a really neat car. Good luck!