I got rid of the light assembly/licence plate bracket altogether because I did not like the mud flap look and the fact the plate kept breaking at the upper bolt slots.
I bolted an aluminum strap an inch or inch and a half wide by 8 inches long (width of an Alberta plate) to the fender, with bolts through the same holes your nuts fell off.
Yeah I just said that! lol
I used flat washers, lock washers and double nuts to lock it on because I did not have any locknuts at hand. Blue Locktite thread locker could be used as well.
Then bolted a handmade aluminum backing plate to the strap so the bottom edge was just above the bottom of the fender. Due to the larger size of an Alberta licence plate (6 X 8 inches ), from the 49 US states standard of 5X7 inches, I had to apply a little muscle of Hoss to bend or twist the top of the strap back until the plate is almost vertical and does not rub against the bottom of the taillight lens.
I now have a pair of dual LED Custom Dynamics Tag Boltz with BRIGHT RED LED BRAKE LIGHTS
( to go along with kc2dgq's signal boards mentioned in his sigline in post 3 above), also with white led illumination for the licence plate.
FYI the fine for no licence plate illumination in AB is $58!!