Another option is to drill all new holes, see photo I marked up. If you really wanted to beef it up, you could weld a piece of 1/4" steel plate on top of it before you drilled new holes. This would give extra surface area which will make it harder for the steel to "egg out" again.
It looks like the bottom piece that the blade is attached to what is egging out the worst though. IF you could weld a piece of steel on it too, that would increase the area that the pin is hitting against. The locking pin is obviously made from a harder steel than what the pivot plates are made from.
Another thing you can do to prevent that is to use two pins all the time, that will double the area where the pins are pressing against the steel, when the blade tries to rotate on the center pivot pin.