I am looking to do some upgrades. I'd like to go with a set of Racing Headers, and full race exhaust. I only drive a few miles per year so i don't have to worry about smog.
You will get a variety of opinions on the subject but, quite frankly, I think the cast iron manifolds look like crap in an otherwise spectacular engine compartment. In addition to the cast iron manifolds, the headers eliminate the very heavy catalytic converters. The weight loss isn't trivial, even if the HP gains are.
4.0 Whipple - Header vs Manifolds
Manifolds/Cats/Ford Racing Exhaust = 735whp @ 23.3psi
Headers/Ford Racing Exhaust - 785whp @ 21.7psi
All other supporting mods the same.
YMMV