Thank you, non-fixie. Having read this nice test I obviously bought the wrong bike, and it confirmed my expectation on the not-so-supersport-weight: 15 kgs! But no rust on my frame, so on durability the test proves wrong imho.
Earlier in this thread you mentioned the numbering system where the first two digits state the year, but cove might have used a different system? Anyway, late 70s will probably be properly dated when looking to the rest of the parts.
What do you think of letters on the top tube? placed by a drunk? Monday morning issue?