derek uk wrote--"it might be a marine manifold?" The manifold in the ad is similar to the one I have available (not the same brand--but made for auto use with a 32/36) -- the mounting area (pivot point) for the cross shaft on both are on the firewall end of the manifold. The shaft may be placed in such a way for the photo so it isn't hanging out the far end (making storage more difficult too) but it seems rather long (at least for use in a 122 or 140 series--my memory of the setup for a 544 is not clear).
I do have an actual B18/20 marine manifold. It mounts 2 single throat downdraft carbs (without digging it out of storage--Solex I think). Available for $30 plus shipping if anyone wants it. -- Dave -- ps--I think I may have too much time on my hands these days :-)