Hi,
I am a new member to the hmvf forums, i have been on it before and came across this thread and just wanted to add my bit to it.
as it has already been mentioned by others that what you have is most certainly a GS Bergen and is a 1980s type the earlier 72 pattern GS Bergen i believe had a different designation and also had different clips instead of pull closiers.They are different to the SAS Para bergen as i believe the GS to be a 75 litre bergen and the SAS bergen to be a 120 litre bergen they both use the same frame, which the one in the pictures posted does not have.
They are quite hard to find and without the frame go for anything up to 20 pounds, however if it is a 72 pattern one it will probably fetch for much more.
Hope this helps,
Lewis