With all the craftsmanship, i'm a bit embarrassed to say I used various sizes of fender washers.
Used either screws or small magnets to hold on to firewall to tack weld.
For the big holes cut out filler out of 18g sheet metal and tack/stitch welded.
You can see the results below.
http://67-72chevytrucks.com/vboard/s...3&postcount=97