Dual exhaust HP increase?

Hey all, I'm very new to the Mopar scene (and the car scene in general).
I recently purchased a 1968 valiant with a slant 6 in it and am wondering if dual headers would be a recommended route to take? About how much extra HP would I receive and do you guys recommend a certain set that I should grab if I do?
Thanks and I look forward to posting and adding/ sharing in the community!

Kyle