1963 Valiant Wagon "Candy girl"

Now to all the extra holes in the fire wall and those elongated fender bolt holes, this is where a thick copper plate works. You put the copper plate behind the cleaned up hole then MIG weld the tin to fill the hole shut. The weld will not stick to the copper.
Then grind the welds flat and redrill the holes as needed.

I used 1 inch copper pipe that I hammered flat on one end and put a bend in enough to hold it flat. Do a hole and let the tool cool as copper conducts heat well and I have burnt my hand when doing too many holes at once.