headers for 1965 6 cyl 200 cu in

I am replacing the exhaust manifold (1965 6 cylinder, 200 cu in.,

3-speed). I was originally just going to replace it with a new exhaust manifold and then I got to thinking about replacing it with headers (I realize I'd have to deal with the exhaust pipe too). I've seen headers for my engine (e.g., Mustangs Unlimited, part BA54) and am wondering whether there is any performance advantage (for my particular engine under just regular driving conditions) or if it is just for show/sound? Thanks.