Figured I would chime in here with my small bit of info. I bought a Dutch grouping, belonging to a 2nd Lieutenant(2e Luitenant) who served in 422IBC, which was a territorial infantry company = 422 Infanteriebeveiligingscompagnie - (InfBevCie 422), in 1985 and 86. I have contact with the vet and have asked him many questions. It came with almost everything, including both packs and straps.
Of relevance to this post, he was issued 8 equipment straps.
His large pack is the rubberized type and is dated 1983(the earliest dated one I have seen, considering the NSN for the rubberized large pack was created on 5th July 1982, this is very early). It came with 1 equipment strap attached to it to carry it like a briefcase, which when I asked him, he said this was how it was carried, normally it was left in the vehicle. His small pack is an old M52 pack.
I then asked him what he used the other 7 equipment straps for, he said 6 of them were for the sleeping bag and the last was a spare I guess. He carried the sleeping bag with the pup tent wrapped around it, on his chest. He said he used 4 straps on the sleeping bag(1 strap won't wrap all the way around it), 2 on each side, linked together. The he said the other 2 were used to attach it to the pack, but I have no idea how that was done.
As for attaching both packs, I too have wondered how it was done, for a while all I had to go on was the photo michel. I asked the dutch group 41dko, I got a reply today with these 2 photos:
So it seems that is how they are attached. But I don't have a canvas large pack and the rubberized large pack is different so I haven't tested it yet. The rubberized large pack bottom loops, on the bottom of the pack that you slip the L straps through, they are opposite of the way they are on the M52, so it might be easier on the M52 pack. I tried it with the rubberized large pack and let me tell you, it sucks. Like really really bad. There is no way this was the way to do it in the 80s. It looks like it might be easier with the older M52.
Oh and they also said the blanket roll was not used past the late 70s, so by the 80s the sleeping bag roll carried on the chest was the norm. About carrying it they said: "It’s called “Suriname rol”. You also just the straps to make a roll and hang it on your “hoekriem” of your webbing." Based on that I came up with this:
I used a UK Pattern 58 Sleeping Bag as a stand in as I don't have a KL one yet. I used 4 equipment straps, 2 on each side. I think this was how its done, can't really find any other way, nor do I see how the 2 extra straps would be used to attach it to the pack.