looking GREAT ! I think most of the people in charge of letters and numbers on bicycles get their training in rail yards putting hood stuff on rail cars. lol
In the second photo there is something on the seat tube. The top photo leads me to think it is a 4000 . I think you got a good buy . I'll bet there is a lot of years of service as a run around go-fer or trail bike. Clean it up and enjoy.
EDIT to add. Check the serial number on the bottom bracket to find the year made. I find that interesting.