You are missing the tailgate cable retraction system There shoud be a wire spool in the fender which feeds a cable out to the tailgate. It is on a retraction wheel. It feeds through a metal formed grommet which fits the hole you are showing and then the cable attaches to a bellshaped fitting on the gate. Also you are missing the "chrome hoop" which engages your lock when you put the tail gate up. This pic is a little small but you can see the cable set up.
I got that off of Google images. I did a 55 Mad a few years ago and I'll try to find my build book. Here's mine......
I just looked at Danchuk Manufacturing. They have a page in their catalog with all but the metal grommett. Parts #, 1058, 221, 221A, 15023, 15022. They are in Cal....
My cat's. an older one. So, I'm waiting for a more current one to come with a pile of parts I ordered from them this morning
Click on this link below. Hope it helps and good luck with your 57 Nomad. I still kick myself over selling my 55 Nomad and this was back in 1983. Heres the link http://shop.oldedaysclassiccarparts.com/NOMAD-AND-WAGON-ITEMS_c24.htm
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