I'm wanting to ditch my OLD low hanging headers, are these manifolds worth it?

I am aware there is a bunch of stuff out there. Unfortunately living in Alaska and shipping an already "out of my budget" exhaust system here is a firm NO GO. I will end up taking the ole' Duster to a local reputable muffler shop for the new system. Just exploring the options. I guess I'm really wanting to know IF these manifolds would rob enough HP to make a difference over headers.
headers will provide more hp, the difference will be how mild or wild your engine is built...