Hi Jim,
Actually, the two shown are not for this car and are for earlier models (E30 and ?, I probably should not have included them on this thread) . They do not have the side port near the outlet which is unique to the '73 and '74s. The '73 manifold, I'm guessing early '73 (N36), has the side port as shown below and in earlier post. As you know, there is a tube that routes from this port up to the balance tube. On the '73 exhaust manifold, I drilled and tapped the smog ports. You can actually see part of that manifold in one of the above pics (3 manifolds). Also, I re-posted the '73 manifold pics below. The '74 manifold are much larger as seen in your picture. Not sure when the change came about for the larger size, but both have the side port.
Yes, funny thing about the air galley and the discoloration. Not sure if there is any way to prevent that. It seems to discolor more if you disable the air pump which probably gets the air galley real hot since there is nothing to cool it down. It does appear that after the initial discoloration that the color stabilizes which is a good thing. And, I really don't have enough experience with the different platers to know which ones have a better finish or not. Will have to see how the air galley for this '73 does as it is NOS. Hopefully that does well.