FYI your 3/4 ton has very little difference to a 1/2 ton. The body(cab/bed) are the same except the bed is longer. The frame is 11" wider at the rear tires on a 1/2 ton and shorter by ____". The front suspension is heavier and a bit different.
I would vote to keep and repair the frame. By the time you finish filling the holes you will be on your way to welding perfection.
