Only cavemen still weld firewall holes. Cut to size patches for all the holes, rough up around the holes on the inside of the firewall with 36 grit disc, rough patch up with 36 grit, butter around holes with 3M Panel Bond and stick patch in place. Next morning your DONE with no warping and about two hours total time. Panel bond holds together airliners and the 2000mph SR71 so it should be sufficient for firewall holes.

Firewall holes "bonded" 25 years ago---had 73 EXTRA holes:
[img]https://i.postimg.cc/rKbQzc92/dan-s-49-011.jpg[/img]


Evan