I've seen the Sterling models like this in late '60s-early'70s ads. Columbia bought the Sterling name @ the turn of the century, during the 'bike bust', when dozens of companies went under. They used Sterling before, in the '30s-'40s, different bike completely though. They also reused the Rambler name on a basically identical model as your Sterling. I'd say most any middleweight Columbia guard would fit, and that red color didn't vary too much. The early '60's models have a cool looking guard w/a fin on it. Typical seat is a two tone Mesinger, the near identical Schwinn branded one is a replacement.