Finally someone states the obvious (to experienced eyes). The ferrules are too large for the casing diameter, they are also brake ones with not enough "base" strength to resist the casing's pressure. Not yet said (I think) is that the casing is rather short. I generally have the shifter to DT loop long enough to almost touch each other in front of the head tube. Last point is that if the crankset is from 1981 the spacing between the rings is likely greater then what was speced about 10 years later (when 7 and 8 speed indexing was coming about). This last detail will compound the cable tension range of tolerance and make chain rub on the cage more likely when in the angled combos. Andy