Stevef,
Now you've said that, I'm doubting my memory! We would open them routinely on the ground to get some air through the aircraft, was it the top, bottom, Oh God, I'll be awake all night........
Perhaps it was at the top...probably, even; I'm sure you must be right. It was the Captain concerned who told me about the exit opened in flight, on the ground after arrival of the flight.
Wouldn't a top hinge have meant that quick evacuation would be slightly less easy?
Incidentally the registration of the aircraft in my pic above was G-AGKE, for those who note such things. I don't know what happened to it; some of them went from GF to Saudi Arabia for cloud-seeding, I think. I have a feeling that G-AMRA, which I last saw at Coventry in 2001 was with GF in the 60's but I'm not certain.