A note about that article also... you have a little bigger cam and a way better intake so the differance in HP from 318 manifolds to headers will be even larger because even more fumes will be trying to get through there.

Your duster is not much lighter than the little dakota either, those dakotas weigh about 3400 typically and that duster is gonna be around 3300, this is of course assumeing both are stockish weight. The dusters gained a lot of pork starting in 72 and got heavier every year till at least 74.