If your manifolds are quite "heavy", you might just have the "good ones". That is, the "long branch" exhaust manifolds that fit 1st gen Firebirds. The plain-jane "log" manifolds aren't heavy at all. Do the manifolds "sweep" towards the rear and then straight down, with a bend that points the exit to the rear? All in all, about 14" long? If so, very few headers are "better" for power, and none will out-live them. If they're the "log" type (a straight "tube" with the ports exiting into it, and a small flange where the "down pipe" or "head pipe" attaches), I would recommend the Hookers. Mad Dog also makes very nice headers for the Pontiac and they fit quite well.
NOTE: If you're not sure about the manifolds being "log" or "long branch", PM me a pic or post a pic, and we can identify them for you. If you DO have the long-branch, don't spend a dime on headers...
I would disagree that Pontiacs are more difficult than "most" to install headers. Having worked in performance-oriented repair shops in the '70s, I put headers on hundreds (literally) of cars. There are two bolts that are difficult on the Pontiac. Those are the fourth one "back" on each side. A short open-end wrench, reaching in from the bottom, is the best way to get those, but the rest can be accessed easily by either a box-end wrench or (even better) a long extension and "wobbly" (swivel) socket from UNDER the car. You should put headers on a '68 Mustang with a 428 CJ in it... (:- or a '69 Road Runner w/Hemi... LOTS of "fun"...!