TA and stronglight chainsets often had such a narrow gap outer/arm that in order to shift on a plain (no ramps, pins or cut teeth) chainring, the cage has to go quite a long way across, often fouling the arm.
Low q-factor was popular.
We wouldn't bother trying to find a mech that works - in some cases i don't think there are any.
If you have a flattish cage from the period, even matching the chainset if it's campag or mavic, that's about a good as it gets.
Where the inner ring was quite large, the cage was fairly parallel. problems arise if the inner is smaller than 30, the cage shape often became more complex to work closer to the bb
When it shifts you'll probably hear the clack, then you just back the lever off a fraction.
If you bend the nose of the inner plate out slightly, the chain will shift earlier, but you'll need to do more trimming to stop rub as you change on the back.