Jordan,
I made a pair of these for my Ford some time ago.
The originals had countersunk hole on rear of the attaching lug, with countersunk screw which almost filled the hole. it was then welded into place, completing filling of the countersunk hole.
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You are correct about the wing nut also.
Don't know how long I left the thread section, but only cut it after I did a trial fit, to ensure enough thread to unwind the wing nut to 'curtain removal' position without falling off. There wasn't enough of the original thread to indicate a correct length