After three years of searching, I have found the Schwinn Speedster 3 speed. This one is allegedly from 1976 and given that it weighs a ton, it probably is. It looks like the fenders are replaced, but the paint appears to be original. I picked this up for $150!
Of course, the seat is not the original blue/white two tone kind, however I imagine I can find one sooner or later. In fact, there are a couple for sale online right now, but not the right shade....