That looks New Idea but looks smaller than the 12A I have sitting here. The tops of the box sides aren't angled and the tongue doesn't have an integral jack. Might be newer. The metal looks like NI, though.
On at least some of them they riveted a serial number to the frame on the right front corner (if you were sitting on the tractor). It should be visible without crawling under it. Just an implement sized tag.