Here are 2 ways of attaching the Jetpack to the harness. 1 way is to directly attach the straps to the jetpack with chicago screws (or similar type hardware). The other is to run the straps into the hollow body of the pack and attach them to the inside.
I dont have any images of my setup handy but I can post some images of the setup that I pretty much directly copied. These photos come courtesy of Seeker, who is actually the maker of my harness as well.
This is the back side of the harness. You wear it over the flightsuit. The straps feed through slots that I have cut in the back of my leather flak vest and then feed through the slots molded into the back armor. I attached the buckles to my jetpack directly using chicago screws and then adjusted the straps to hold the jetpack up at the correct height on my back.
This is the front of the harness. Velcro straps wrap around the ribcage area from the back and attach to the front securing the harness on you. I set a heavy duty snap in the hanging straps which snap to my cod/holster/thigh plate assembly which keeps that from sagging out of place.