I've found the exact fasteners or buckles or similar here in California, could be CW era but I don't think so.
It looks like you've found a Georgia Frame Buckle.
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The basic design is the same, but I didn't see any with the gutter back.It looks like several at the link that Fullstock posted, so it could be. What is the height and width, and how long are the prongs?
I may be wrong, but I don't think the Georgia style frame buckles had gutter backs.