After studying the drawing in the competition manual, I would say that this manifold is the original Datsun competition item, part No. 14002 - H2310 & it was intended to be fitted with Mikuni Solex N40PHH-30 carburettors.
The linkage looks to be mostly original too.
Note that it does not use the top outer mounting studs that oval port manifolds usually use, but the center one instead. [See photo below, right]
This seems to be unique to the original Datsun competition units.
So to answer hillbillyhectors question, it was originally made for a 1200.
A 1200 GX competition engine that is.
I think that what you want is one of these.
so check out
this place as he has the one in the photo.
If you need one for an oval port head, well he has that too.