Honestly it's tough to say how much of an improvement over iron manifolds these are and whether it's worth the hassle of fabbing custom downpipes. I actually bought them because one of the iron manifolds I intended to use at the time turned out to be cracked and I didn't want to use tiny restrictive 318 or 360 manifolds.
I see posts about that AutoZone discount from time to time, how does that work? Do you have to be some kind of "member" or a part of some rewards program? TBH I never go to AutoZone lol it's always Advance or O'Reilly for me, or if I need something actual decent quality and can't wait to order online I'll go to NAPA.