From the pictures of the bent Reese snap up bracket, this looks like the classic Reese snap up bracket failure from heavy tongue weights when the bracket is not bolted on.
It has occurred many times before on loaded tongue weights of 1,000# and over. In certain turns, the loads on the inside WD bar go real high. The heavy tongue weight coupled with 1,200# or higher WD bars has been known to spring open the top of the snap up. If they are bolted on, then this does not happen. If and when you bolt them on, make sure the bolt is touching the top of the hole in the bracket so it can't slip down.
I used, 5/16" carriage bolts that fit in the square punched holes to bolt mine on. Your vintage may or may not have the square holes, then just add them as round holes size to size with the bolt.
Page 5 shows the bolting if yours does not have the holes. They just do not go into why you need to bolt them on and what the issues are if you don't.
https://www.reeseprod.com/support/installation/N66022.pdfYou should get your tongue weight when loaded checked so you know what it is.
I agree, fix the frame as leaving it like that is a problem that sooner or later will become a problem.
From here, by the pics and the amount of cracked paint and rust under the top of the bracket, this problem existed a while ago. If you just bought it, you inherited the problem from a prior owner. I do not think this was caused by over tightening the bolt.
Hope this helps
John
PS,. Reese now offers a heavy duty snap up with gussets welded on the side. I myself would still bolt it on.
