D.O.,
Apologies, I skimmed over this:
Two aircraft heading towards each other in each pilots one o'clock. Not quite likely to collide but too close for comfort.
Left or right, climb or decend or pull the BRS?
Is this scenario in the ANO? That question is for those who do take it to bed at night.
It's very simple. If they are each seeing traffic in the one o'clock position, the relative bearings should be changing, and there is no risk of collision. They will pass starboard to starboard. This is in the ANO.
This is not necessarily true if either aircraft is manoeuvring towards the other; the rules do not provide for manoeuvring cases.
Again, the maritime world makes much more of the very simple interaction between nav lights and traffic lights. The situation above (green to green) is safe. If you see a red nav light on a constant relative bearing, you must give way ('stop'). If you see a green nav light ditto, you must 'stand on' (maintain course and speed). Why the aviation world has never cottoned on to this is beyond me...
There's an excellent little book called 'The Seaman's Guide to the Rules of the Road', which examines the relevant rules and their interpretations. Sadly, there is no aviator's equivalent.