Headers for a A body

1- the car already has headers on it? then unless they're literally falling apart, destroyed or rusting off leave them on and use that money elsewhere

2- you don't need headers for the kind of build you're doing. if you want headers, that's fine but they're totally unnecessary for what you're building and the gains that you're going to get for the money spent are minimal.

look at the dyno charts from the article @273 linked. from 318 manifolds to 1 5/8" tti's you're giving up 15~20 in tq & hp in a fairly narrow range, and then the numbers fall off abruptly at about 4500 due to the cam (basically a 360 2bbl). that combo also has what appears to be a demon 750 double pumper with mechanical 2ndaries, where as you're talking about running a 2bbl or a smaller 4bbl on a less aggressive intake, different, likely smaller heads, and probably smaller cam, with likely less compression. which would mean even less gains.

do headers make a difference, yes. do they make enough of a difference on your particular combo to spend that kind of money? that's for you to decide. but dropping a smooth G for 15~20 bragging ponies isn't my style.