Old Henry, I stillc ant believe that I couldnt figure out where that piece went. I think since it wasn't all bolted together and we were just setting things where we thiought that they were supposed to go, that without the radiator bolted in place, it didnt make any sense.
And also, my idea that the previous owner didn't know what he was doing holds true with evidence of that picture. Who tears a car apart and then primes that piece only? Of all the different pieces that he could have sanded/primed, why he did that piece shall remain a mystery.