Welcome, Compay!

That's an interesting bike you've got there. From your description it sounds very much like it dates from the sixties, which which would mean either Amsterdam or Groningen. My guess is that '60' and '73' are the down tube and seat tube angles. If the decals are original, I would say 1968 or later.

Could you post more pictures of the details of your frame? Nice big pictures of the frame details would really help us with the identification.