Well, again FWIW, I will say that I have a beautifully powdercoated exhaust manifold, never run since coating, sitting in my garage. It's off of an E36 M42 - the flange bolts perfectly to the exhaust ports on the head, but the collector end is off enough that it definitely doesn't fit.

It's in the FS section now...
This header looks to be a different animal entirely, as the pipe comes down too far to join the cat at the stock location.