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

Those are 318 stock manifolds. You can put a ten foot diameter pipe on them and it won't make a hill of beans difference, since they are attached to about a 1 7/8" outlet. Don't waste your money on big diameter pipe if you're not going to at least find a set of the 68-71 340 manifolds so you can take advantage of the bigger pipe.