Here's an original - as far as I can tell, it was a phosphate finish (no evidence of cad or zinc iridite), either plain steel or phosphated nut and washers. Bolt is 1/2-20, 4-13/16 length under the head. Only marking I can see (sorry for the rough finish) after beading is an "L", which I highlighted best I could for the pic. I have both sides, they are identical markings and specs.
Hope this helps -
Regards,
Steve