I would never drill one of these. But someone did...
So I've got this old safe that has multiple holes front and back. The holes are actually visible, serving as a landmark should anyone desire to drill it again. And as I suspected, they were filled with something nonmetallic.
I took a punch and a hammer and the filler material popped right out on the first tap. I followed that with a powered brush and cleaned it up in preparation for welding.
I filled the holes with a combination of A36 scrap, hardened drill bits, and welding rod stubs. The idea is to have a bit of a heat sink so that I can make the first pass very very hot. After the first pass fused everything, I followed up with 6011 rod cold and slow (50 amps) so as to deposit an excess of steel that I can grind flush and smooth and make the repairs invisible.
I started with the back, because I figured it'd be the most forgiving and the least critical and I've never repaired a safe before.
I fairly happy with it so far. I'm going to remove the lockwork before I repair the door, and I've got some hardened roller bearings I'm going to use for filler on the door.
Macneale and Urban went out of business in 1903, which makes me suspect the presence of asbestos.
I welcome any comments or criticism.