Anyone who thinks a lead repair isn't permanent doesn't know how to do it correctly. Even "waterproof" fillers absorb moisture over time. Filler is a finishing aid, not a solution. Filler over a whole car? Fuckin hack bullshit designed to make TV viewers spend money on product. Design studies cast in epoxy and tooling foam need a layer of "frosting". Real cars do not/should not. If it were my truck I'd go for making a repair panel, but the challenge is the strain in the area. I see a cowl vent involved, I see some structure behind, and my concern would be where it goes when that's "relieved" of it's structural integrity. The holes are bigger than I considered, but not impossible to solder in. I agree with the knowledge gained in forming your own panel, I experience the satisfaction of such multiple times a year due to my profession. Not everyone has that so you make adjustments as you go. The danger in a lead repair is as I stated up front. Remove the acid from tinning and it's there forever. There's lead seams in every 1934 Packard closed car that I've done, many of which still have their OEM lead in that seam. I suppose some day it will fail, but 79+yrs isn't too bad of a longevity score, is it? Just sayin...
How about taping over the area, fiberglassing a layer of mat over it, pop that off, set it in a wood box filled with more resin or bondo and beating a patch panel into that?
just start bending some metal already. you are not committed until you cut out the damage and strike the first arc.