I have gone thru this repair and is not an easy repair, but my car was in bad shape.This shows the damage and the cut lines to remove the damage.
damage removed
patch panel fitted ready to tack
body mount fabricated
zink primer where the body mount mates to the inner wing. I made the bottom of the body mount stronger using 11 gauge where the body mount bolts to the frame.
body mount plug welded to the inner wing welds
welds ground, hammer and dollied and body filed. driver side same as above.
Hope yours is not this bad, Good luck, Frank