Umm, yes, I was not awake enough when I wrote. I forgot the ball was in the arm not the link. Been this way since 77 in Mitsubishi's in the USA and since 73 overseas.

The socket you installed should not need gussets with the change you made.If anything you could strap the end and taper the welds down the sides. The only real critical area is at the spline end.

Reflowing a Mig weld with Tig is a rear PIA since the Mig weld is full of inclusions. The puddle gets real bubbly and never really cleans out. Some guys can do it I guess but I am not real satisfied when I try.

Do you have a gas grille on the deck? They are great for preheat work. A small part like the arm you are working with will fit in a toaster oven.