I’m using the z-library app. It does the searching for me :)

Depends what you mean by human. If you restrict the term to homo sapiens you put yourself in a small minority. I’d say the fact that these people used tools in a sophisticated way pretty much defines them as human.

What then? Aliens? Sentient ants?

Welding will distort the steel. It’ll no longer be straight. Steel is pretty cheap. Find a metal supplier near you (not a big box store) and buy the angle you need.