Yes, Chris, on reflection these holes must be a production item rather than something for the end user to actually utilize. Probably helped stabilize the rectangular steel blanks during the stamping/forming process.
On the NOS one, you can actually see fine, parallel stress lines running perpendicular to the major curves, and when I think on it, I have seen a lot of these plates over the years that have failed by the web of metal to the outside of the main belt screw hole, cracking off. The crack lines would be parallel to these stress lines. Maybe it pays not to overtighten the burled nuts.
David
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