Some places have specific requirements to meet fire code when filling that space. For example, where I live you can't just place insulation bats between the studs because the narrow gap that would be left between the bats behind each stud is considered an airspace that could allow a fire to transit to the floor above. I do live in fire country and using bats doesn't look practical in your situation, this is just an example. I would just double-check the fire code to make sure that exactly how you are going to do it won't run afoul of that.

So much this. I can't believe how many highly educated and smart people, some in biological sciences, can't accept that many traits appear for no reason and don't disappear because they have no reason to. My advisor used to say, "evolution doesn't have to help you to happen; it just can't kill you or make others not want to fuck you".

Others have said it but I'll agree - this is almost certainly not worth the effort. You'll have to put in a lot of effort to avoid inhaling fine concrete dust at best or lead at worst and the only thing you'll learn is that concrete that old is incredibly hard and that jobs like this eat through grinding wheels and are incredibly hard on your elbows, shoulders, and ears.

But my libertarian friends assure me that their metaphors about people using credit cards and global macroeconomics and government debt are perfectly reasonable and not at all childish oversimplifications.

Microscope got me.