Hedders on a Pontiac is quite a bit more challenging, than most others. Mainly cause of the exhaust port angling towards the ground. That's why I believe in most street applications the RA manifolds make more sense. For many benefits. But if you're lookin for that all out bit of necessary power, (and image), hedders for performance reign. Nothing like the sound of a set of open hedders on a sunny spring day.
The 1st thing needed for Pontiac V8 hedder installation, is a yard of patience. (Seriously) Especially if you're not a professional. Next will be some very long 3/8ths extensions, and possibly a wobbler to fit them, for getting at the back cylinders from below. That way you can use a ratchet, rather than open end wrench. And have some stubby open ends, and maybe even some cheap Chinese ones, that you can bend a slight angle into. And your flange gasket, you can cut into 3 sections for each side. Separate the frt, middle and ends from each other. Then slot the bolt holes under the ones that aren't already. And the bolts should be specifically short hedder bolts, 6 pt 7/16th, with the small diameter built in washers. (Not sure if 3/8ths size heads are available, but would be better).
Depending on the make and fit of the hedders chosen, will determine how many accessories you'll have-ta remove, to get them up into place. Start with the frt bolt 1st, then the fwd bolt on the rear cylinders, and only catch them by a thread or 2. That was the easy part. Next you'll need-ta squeeze in the rear bolts on the frt cylinder, and the rear bolt on the 5-6 cylinder, where the tube is bent right smack in the way. Twist them in a few turns also. This is where patience, and the short bolt really shines. And finally the rest can be installed, from above and below.
Next is when you just simply slide your individual gaskets in from above, and not have-ta worry about alignment problems with bolts holes, if you didn't separate them. Once they're in, you can begin tightening all bolts, remembering that the ones above the bent tubes, (1-2, + 5,-6) will need-ta be tightened simultaneously 1st, then the rest randomly.
My preference "ust-ta-be" using the factory metal exhaust gaskets in the Fel-Pro kits, cause they would last yrs, before rotting out, where the Mr.Gasket paper ones would blow out every season. Course, this was when we drove our cars every day, as daily transportation. Car-port queens might last quite a bit longer.
That's about all the basics I can remember, but with todays new aftermarket stuff, maybe things have changed, hopefully for the better. Hope some of this helps, along with the other advisors.