All good leads but the reality of this situation is dominated by the many, many varibles your particular car layout requires. Shelf stock shortie or blockhugger styles may work, but are a compromise at best. (I've found on Cobras.) Exhaust performance on Cobras is DOMINATED your side pipe design or exaust systems design. No header design will be effective unless you keep this in mind. Re; headers, generally, the longer longer the runners are, the better off you will be. But that is a hard thing to do on a Cobra.
I've built several 385 style engines for 3 different Cobras down through the years. In each of those builds, a custom set of headers that was unique to that build was required. And that's the long and the short of it in my mind. To do it right, you are going to have to bite the bullet on this one I've found. Anything else is just a compromise. You can however price shop this one, of course. And if you are any good at welding a custom set is not a terribly hard thing to do. Each set I built took about 8-10 hours to build. Parts can be sourced locally or through
www.headersbyed.com
Cobrashock