I got my first welding machine today!! Super excited. And yes, I know how to weld, just never had my own machine before. Going to school for it in a few months as well so thats a big plus
Basically on the 4th gen 4Runner if you want to fit a tire bigger than 33", or even some 33's, you need to cut the edge off of a body mount then weld on a filler plate to keep it strong enough. It's just a way to gain an extra inch or two of clearance.