I am sure this is a tailgate for a 55-57 sedan delivery in spite of the description!
https://www.facebook.com/marketplace/item/327838539618684
It appears you are correct.
Here's a '56 to compare (courtesy Flickr):
67 Chevelle Malibu Sport Coupe, Oshawa-built 250 PG never disturbed.
In garage, 296 cid inline six & TH350...
Cam, Toronto.
I don't judge a man by how far he's fallen, but by how far back he bounces - Patton