This rucksack seems to start being issued in the mid to late 80's, mainly to the Portuguese Rangers (Special Operations).
The construction is a mix of old and new, a very light nylon fabric was used for the main body, pockets and flap. Leather was used on the reinforcements and some attachment points, some closing straps are made of leather and other are made of webbing and seem to have being M64 parts re-used.
Another peculiar feature is that the closing flap is not integral to the main body.
This rucksack lacks integrity, it is simply a kind of very light duffel bag with pockets, attachment points and straps sewed on it. It is very uncomfortable to wear and it is very strange that OGFE made this kind o rucksack when there were very good alternatives on the market.