Disassembled the BB and HS. Using the proper tools (Campy BB spanner and Hozan fixed cup remover) everything came out flawlessly. You can tell the bike was properly assembled as the threads were chased and BB shell was faced, among many other details.
The BB grease is different than that of the HS (translucent green, vs. off-white paste), so I think the BB was serviced once.
Given the condition and clues around the bike, I think it was ridden during the 1970s. There are normal chain marks on chainstay, and indication of a dropped chain here and there. I think it was likely sent for a good tuneup in the 1980's: New Weinmann brake hoods, serviced BB, a clincher wheelset with upgraded 6spd Ultra freewheel (still 120mm spacing), new tires. The tubulars were probably a real hassle. TBar tape was updated - It is black, with some of the original light grey still peeking through under brake hoods. I think the bike sat there since then: The tires are dry rotted but still unworn.