Headers vs. Manifolds

Ok here is my opinion.
1) The 383 is a big-bore/short-stroke/high-rpm brawler. You already have everything it needs and wants. IMO, it would be a shame to stifle it with the logs.

2) If you can hear that it has a "fairly radical cam" in it, but you stifle it with log manifolds, then IMO you would be better off going down about two or more cam sizes, to get the pressure up, so you can run the 3.55s, and run a lower-stall convertor, and have a strong bottom end.
But when this is done, you gotta plan ahead so that your pressure does not rise high enough, to put the engine into detonation at WOT.

3) If you're taking it apart anyway; It ain't a lot of work to stuff a 440 crank into her.
IIRC that would make her a 425 low-deck before boring. Heckuvathing that would be in the Duster, even with logs and a 2-bbl cam.