May I be the first to thank you for your information, Glyno. The route on the map you posted shows what I expected from your earlier description of it.
All the accounts I read before I attempted it said that you contour around the slopes from the 'notch' on the North Ridge to Bwlch Moch, which I can now see is a bit misleading, for I tried to take a more direct route from one to the other rather than turning sharply back parallel with the ridge.
If I had overcome my nerves and succeeded with my wrong way I would have overshot Bwlch Moch anyway (which wouldn't have hurt, though, for I was headed for Pen-y-Pass).
EDIT: I looked again at the information I had, one of them says the path goes around the mountainside at around the 1,400 feet contour, 427m in today's money, which if you look at the map is quite inaccurate.