I personally never saw anything wrong with the original pin design. Pin can't turn, because it's set with a spirol pin. As long as the axle gets greased, it was a good design. Yes, the bolster can spread.... but only after years of use. Even then, I never thought it bad to bend back, or even shim up with washers to fix.
On the bolt deal, welding a nut on and using a lock washer would be fine. Shouldn't back out. Set screw idea looks like a lot of work.... plus, we have all seen how troublesome PTO's can be to remove. I don't care for set screws. All just seems like a lot of work to fix a non major issue to me.
