I think it likely that 'killing floor' was originally that part of a slaughter-house, but became a kind of metaphor that spread into more general use - including into places far from the 'packing' industry.

"drifting door to door"? That's what we would call "couch-surfing" today. Or just begging and/or looking for work.

("dry so long": would seem a typo or error in transcription?)