'71 GMC 2500 exhaust manifold (350) interchange.

[W. Higgins]

My left exhaust manifold is broken. I thought this was going to be a simple RockAuto thing. They don't list any left manifolds for '71 GMC 3/4 tons. I thought this was a simple oversight, so I searched the same for Chevy and get Dorman 674-201. Sure enough, on the interchange list this manifold fits every GMC over and below (1/2 ton and 1 ton) but not my 3/4. It looks like the manifold shown in the photo with the curved 3-bolt outlet. The Dorman site provides the same information. What am I missing here?

The only other clue I've found is this outfit lists a curved outlet manifold like Dorman's and like what I have on mine:

https://www.1aauto.com/chevy-gmc-exh...iABEgJIUPD_BwE


.... however, they also list a pair with a straight dump for the same application:

https://www.1aauto.com/chevy-gmc-exh...SABEgK3jPD_BwE


Am I getting bit by some kind of mid-year parts change where the books might not be up to snuff?