OK, here's that fat exhaust manifold off the Fordor. It's the bottom one in the picture. The one on top is the standard T manifold.
Looking at them carefully you can see that the odd manifold is straight edged on the top while the standard one has a slight curve. The odd one is generally a little heavier. Where you really see a difference is in how wide they are.
It doesn't show well here because of the camera angle, but the width of the standard manifold is 1 7/16".
The odd one measures 1 11/16". I call this one odd because it's the only one I have. I have four engines which all have the other type, plus another half dozen loose ones. Can anybody ID the oddball fat one?
Steve, have you checked the port alignment on the original manifold? I'm not positive, but I think the original manifolds should be straight along the top also. They get warped that way from usage. I wouldn't be surprised if your manifold has a bit of warp to it. I have never seen a NOS one though, so I may be all wet. Dave
It's got an "M" on the casting, must be for a Metz.
I believe that it is an accessory heater/manifold, flat to accept a cast accessory heater on top.
Dan, I was wondering that too. The metz intake and exhaust manifolds do fit on the T. I am running a metz intake on my T. Larger cross section/bore but fits perfectly. I wouldn't mind finding a metz exhaust manifold to try out one day just for kicks.