Where this is plug welded I would tig the part so I have better heat control during the work. The arms have a decent alloy for welding although I have not sent any out for analysis.

I will not get near a structural part that has been Mig welded, I just do not want to learn if it was done by a pro who understands the process or someone at home with a little 110V box.
The weld on that arm look like they were done at home.

Can you not just ream the hole in the arm to what you need?

One thing I get into building Rally cars is elongating the slot in the joints to gain travel. Many of the rubber boots are available to close the joints back up.
Unfortunately the only off road trucks I get recently are Land Rovers and they are weird, or is that the owners are?