I’m leaning towards a set of dorman manifolds
Dorman manifolds made in China will require rework before installation.
Dorman manifolds made in Viet Nam are even worse, and should be returned to where you bought them from.
I've never seen a Dorman manifold that could be installed "out of the box". At MINIMUM, you'll be checking the exhaust passages for iron boogers--casting flaws where iron escaped the mold and is hanging out into the exhaust stream--and grind them out when found. THEN put a straightedge across the gasket surface where it bolts to the head to see if it's even close to straight and smooth. Every one I've seen needs a trip to the machine shop to be planed. They've all been warped, most of 'em have rough machining of the sort that a proper machine shop wouldn't let out the door.
My machinist says he doesn't know how to plane a surface and leave the surface that rough. His equipment couldn't do that poor of a job. As for the warpage, I think Dorman's supplier machines the manifolds before they've cooled and "settled", so they're probably flat when they come off the manufacturer's grinder...but subsequently warp after they've been planed while they're "in shipment".
After rework, THEN you can install 'em.
Wild Guess with no evidence: You can buy other aftermarket exhaust manifolds, but they're all cast and machined by the same incompetent company, they'll all need rework.
Genuine GM replacement manifolds may--or may not--be better.
