Quote from Buenos Aires:
I threw my old 707 manuals away, sorry, cannot recall more details.
Tsk, Tsk!
[Mine are somewhere in the garage...] Your memory is in line with mine, though. The 707 Dutch-rolled at the drop of a hat on the approach, as you say, if the Y/D was switched off. But not seriously.
The VC10, if all 3 Y/Ds switched off, was still fine on the approach. But at high altitude it could be quite vicious. One of the items on the conversion was to allow it to build up to about 40 degrees of bank from side-to-side, and then recover manually... [In case anyone wonders, manual recovery is by aileron.]