Can anyone tell me what this is on this manifold?  And what is it used for?  If I have not use for it should I just put a plug in it? for.

Melly;  A few years ago I found  a  International, one ton truck that had a ford engine in it. It had  G heads and a four barrel manifold.  The markings on the manifold where of International.  I looked in the hollander exchange book for 1962 and it listed that international offered a ford  Y-block.  This was in  one ton, four wheel drive Unit. I still have the heads they are G- Heads. But they are little different.
I checked the thickness and they measured  1. 06 thick. The exhaust manifold on the drivers side had a IH number on it. But it was the same as the ones that go the 55,56,57 T-Bird for the steering colume. When I looked at the block it had been bored .080 over , and had a hole in the block. This truck was in a wrecking Yard in Orland  California.  I did save the heads, manifold,  Dist, Carb and air Cleaner.    Bob