F/O limit was 600m RVR or better (CAT 1). Anything less was a P1 landing.
...............if my memory serves.
And, yes, in better weather, P1 would fly the approach with the aim of P2 landing off the approach. Captains, therefore, had the same practice as P2s at flying the approach. In the late 70s/early 80s most of the captains were certainly up to that, in terms of ability. Not so much so in the early 70s.
PS - I seem to recall that P2's x-wind limit was 2/3 the aircraft limit. Not sure though - anyone remember?