I can sympathize with anyone struggling to get the right parts on their car- it can be an ordeal, and we don't really need the grief when we're building our Firebirds and T/As to enjoy life anyways. But I've also heard plenty of horror stories too and been jerked around a few times too when it comes to parts, so I feel your pain.
I lucked out 20+ years ago when I ordered a set of Hooker comps for my 72 Bird- they went right on the 400 w/ no problems, cost like $100 + shipping (I know they cost more now), and made a noticeable difference in power. If the price goes up any more than the $400+ they want for cast iron headers, I'll just get a set of Hedman 28150's and have them ceramic coated- about the same price, but lighter and make more power.
Geno