snap coupler plow questions

I have found a snap coupler plow here locally and am thinking about buying it. I am trying to find out what size and model it is. It is a two bottom. It doesn't have the later pieces that attach to the snap coupler arm latches, but the older type where you remove the latch and slip the piece on and tighten the set screw.  Also the end that goes into the snap coupler bell has a homemade "ring" welded on it. It looks pretty crude and needs some improving. I was wondering if this was an older plow that was maybe a pin hitch that was converted to the later snap coupler type. Is there a serial number plate on these plows to find out what model or any other info? Also, how do you go about measuring a plow to determine what size it is? By the way, I know very little about plows. I've never plowed in my life.

If you buy it get rid of the slide on couplers and put latches on the lift arms. It is not safe to operate the way it is. People have been seriously injured with that setup. Bob