Some info from an old R***it thread (redaction mine, anticipating the site filter) about possible manufacturer:
"During the early 1970s, (while Nishiki was still selling Kawamura-built frames under the American Eagle label), Campania was a Italianate marque (complete with red-white-and-green colour scheme on the decals!) used on another series of Japanese bikes. If your frame has double-butted Tange or Ishiwata CrMo tubing, an integral derailleur hanger, half-chrome stays, etc., then you own one of their higher-end offerings, such as the Campania Pro. The Campania line roughly paralleled the Nishiki/American Eagle, Fuji, etc. lines."