Given the paint quality, seat tube panel and frame material labels, the OP's frame could be one that was repainted by Trek in the early '80s. The rear brake cable guide braze-ons are also of interest. Looking at bike in post # 4, it appears the '78s would have had clips. Maybe the original owner opted to have the guides brazed on in-service, and had the frame resprayed / rebadged at that time.