Corvette had some stainless steel exh manifolds that were made in the 70's & maybe in the 80's. These were supposed to be the best flowing sbc manifolds mfg by GM. Lingerfield(sp?) uses them on his super Vettes.
They appear to be not as sought after for I bought 3 prs for less than $75 each. I try to use them on all my projects if they will fit ...if not I use Sanderson.