My apologies to all for the late late reply (I didn't have my notifications switched on!!)
And a huge thanks to all in this thread!
You guys ROCK. (Only a slight pun intended)
Several of you came back with Crib Goch - having a look around the various 3D maps, I think you might be right there: there's a prominent jagged lump like the one he's standing on situated just above the Cromlech Boulders, such that if you position yourself there with something like Google Maps you essentially get the same view up the mountainside... I'm definitely going to try get to the same spot - will report back!!
For those who asked, yes, my father was something of a climber in his younger days - some of the higher peaks around the globe, and around the same time as this photo was involved in geological surveys of previously unmapped (to a high degree) Norwegian Fjords etc. He apparently used to get up to the Snowdonia region about once per month all the way through college with an equally adventurous friend.... so I think he might have picked the Cromlech Boulders as an attractive place to stop (the climbing area is right beside the road - quite a magnet for boulder-loving types). It then also makes a lot of sense to then imagine he and his friend deciding to scramble up to the prominent cluster of rocks directly above the boulders, to catch a better view of the mountains, then snap that shot.
Anyway, thanks again to all who contributed - I'll be sure to post a sequel shot if I manage to find a way up to the same position!!
(To be continued.....)
D