This bike is at my brother's home in SA so I cannot measure myself. Ordering some bike parts for this and another bike. Looking for a seat stem for this bike. Did these early cruisers come with a 1 inch or 7/8 seat post?
All of the electroforged Chicago Schwinns, including your 1978 muscle bike, took 13/16" posts. Only the brazed models from "the Cage" had anything different.