Ok, got something for ya.
Basically...go buy a couple yards worth of 1 inch strapping (found near fasteners at Joanns). Take the piece of strapping and wrap it around your chest just under your pecks (so it's on your rib cage) and have it meet in the middle. Give yourself about 2 inches on one side extra and 6 inches on the other side extra. Pick up 3 clip kits (found near the strapping). Feed both sides into their respective clips, sew the one with 2 extra inches down to itself so that it stays attached. The other side with the 6 inches is your "adjustment side" that allows you to pull the strap tight across your chest.
Make sure you use a lighter on the ends of all your cuts so the strap doesn't fray. Just burn it for a couple of seconds and wait until it cools before you touch it.
Now, put the chest strap on, and tighten it up. Make sure the chest clip is centered.
Take another strap piece and pin it to the front of the chest strap so that it lays up over your shoulder and down your back. Where you pin it in the front is where it will be sewn. Now, mark where it hits the back of the chest strap and cut it off there. Pin it to the back of the chest strap so it now looks like suspenders attached to your chest strap. You'll sew that strap there and repeat for the other shoulder strap.
Congrats, now you have a man bra.
Ok, now after you've sewn all that, put it back on again, tighten it up. Take a small piece and sew it across the back as a "reinforcer bar", basically keeping the shoulder straps from falling apart.
Now, with the leftover clips (should have 2 sets) one side will attach to your backpack...that will vary on how your pack is made...but the best way is to sew a small piece of the strapping to one side of the clip and screw and glue it down to the pack (I can get a pic of this later when I get home).
The other side of the clips need to be put onto the harness. Take two 6-8 inch strips of strapping and sew them just above the "reinforcer bar" or whereever you want the pack to hang. Keep in mind that where you sew determines how far up they adjust. So just above the shoulder blades is probably the best place. Only sew about 1 to 1 1/2 inches of the strap to the harness with the rest hanging down towards the floor. Feed your clip onto this and you should be finished.
The vest will need holes cut in the back for the clips. Best way to do this is to wear the harness, ajust the "back clips" as tight as they can go, then put the vest on over top. Have someone feel where the clips are and then mark out a small rectangle hole for the clips. Cut that out and sew around the hole to prevent fraying. Then put it all on.
Before someone zips up the vest, they'll need to push the clips through the holes in the vest. Adjust the back clips so they hang down a bit. Then clip the pack into place and pull the straps on the back clip until it's tight.
That should hold everything in place.
If your backpack is too heavy, this technique may not work for you. This will only support a certain amount of weight...but I know that it worked for Runi Netra and his big "sandtrooper style" backpack as I helped him make the harness.
Hope that helps.
