My 1650 had that same failure. The former owner allowed the pivot pin to slip out of the rear socket, which allowed the axle to rotate back, ripping the front pivot socket right out of the frame. I was going to have a new socket made out of a piece of 1 1/4" steel rod, 1/2" thick, drilled and honed to size, then welded to a piece of 3/16 plate steel, which I would then graft into the frame cross member.
The pivot pin is actually held in place by a rolled pin which passes through the front socket and through the pivot pin. These failures happened because the rolled pin slipped out and the pivot pin worked its way forward, slipping out of the rear socket. With the repair you are showing, there is no way to retain the pivot pin, so the same thing will happen again if the repair is not redone properly.
This seems like a very good reason for me to buy a mig welder. Always looking for good excuses to buy new toys...er...I mean tools.
