Here are some pictures to give a better idea of what I did. Pack modification is limited to changing the main buckle on the waist belt.

- Pack with Aarn pockets in place
- Pack with Aarn pockets.JPG (120.72 KiB) Viewed 2393 times
The shoulder strap attachment is easy - it just hooks under the 25mm webbing used by the chest strap of the pack. It is free to slide so no weight is transferred to the shoulder straps.

- Upper shoulder strap clip.JPG (123.34 KiB) Viewed 2393 times
The second attachment is a small elastic loop that I hook over one of the waist belts buckles - its job is to stop the pockets swaying and it does not need to be firmly fixed - I just hook it over a buckle so it is easy to remove.

- Elastic loop stabiliser.JPG (72.68 KiB) Viewed 2393 times
OK now the only tricky bit. The pockets if loaded can weigh 6kg or so and all the weight is transferred to the waist belt by the buckle.

- Typical Aarn buckle.JPG (72.55 KiB) Viewed 2393 times
Aarn uses a rather small buckle but a 50mm version is available. The bottom of the metal strips from the pockets slip into small pouches either side of the buckle and are held in place by a press stud. I had to add a press stud to mine.
The Aarn buckle does not provide any friction on the belt like a typical pack. Initially I removed the wing parts from the buckle by popping off the 3 black rivets you can see in the picture running vertically. I simply threaded them through the WE buckle and used a pop rivet tool to fasten ( you need to back up both sides of the rivet with small machine washers to increase the surface area and not have them pull through the plastic). The WE buckle always slipped even when it was new but this was worse needing tightening every 15 mins. To solve this you could add a "triglide stopper" (my nomenclature) - my solution to any waist belt or strap that tends to slip:

- Modified triglide buckle.JPG (76.65 KiB) Viewed 2393 times
Triglides are built to have 2 thicknesses of webbing running through them but this mod only had one and then a heavy duty cable tie is fed through to increase the friction between the webbing and the central bar - it locks up pretty well - you tighten the problem buckle and then cinch this up against it as a backstop. You could use it on any slipping waist belt.
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Ultimately I used a different method - the WE pack is unusual in that the waist webbing goes through the main buckle at the front then loops back to the hip area and goes through a metal loop - this gives a sort of pulley system with 2:1 purchase to tighten the belt. Because of this it worked better to add 2 of the triglide stoppers here and not have any friction at the main buckle but this is not how most packs are set up. Other solutions might involve a different buckle - an eccentric cam buckle or a 2" fixlock buckle.
HTH
Chris