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I was able to put together a stripped lower receiver with the lower parts kit in one hour. My background in firearms is from owning a pistol and a 22 magnum bolt action rifle.

It is trivial to put together a lower receiver. You can do it with a hammer and a roll pin punch (and you really don't need the punch).

There are numerous vids on how to assemble a lower receiver and how to mill out an 80%. You could even buy a polymer and carve it out with a knife, if you felt so inclined to do so.