I agree with Schlepcar. Try to find someone with a stud welder, that would be the best, Or If you can find someone with a Mig welder try this..I ran across a similar problem with a 64 Riv years ago. I used my Mig welder and welded some scrap 1/8 inch rod together to form a
T, I made 4 or 5
T's and welded them along the area and heated the area with some Propane gas and very slowly worked out the damage by pulling the rods. I had a pair of welding gloves on as those
T rods were getting HOT. Once the damage area was pulled out enough I cut off the
T rods, ground down the high spots and board sanded the area with 80 grit paper then added a skim coat of body filler to hide any imperfections. Then finish off with 150 then 220 paper then give it several light coats of primer. This work is very time consuming, so plan a full day to do the work. Keep the work area clear of anything not related to what you are doing and make sure any combustibles are away or outside of the garage. Working safe is a priority #1
DO NOT use MAAP or Oxyacetylene gas as they are too hot and will burn thru the metal and cause major damage.
Tony