I see stays that are crimped and spotwelded to stamped rear dropouts. Steel, cottered, crankset. Rear derailleur appears to be a Shimano Eagle with the integral bash guard. Brake safety levers. Stem mounted shift levers. Nutted hubs. Everything points to an entry/hardware store level, boom era product. While that dropout attachment was not unique to them, it turns up most often on Bridgestone manufactured bicycles, so I'm also leaning towards a Japanese origin.