I bummed an old World Famous "Mont Blanc" Pack and have stripped it to the frame and plan to build a pack around it with various materials. I'd like to make it possibly a modular system, with various bags that can be attached on depending on the load.
I am considering trying to make some of it with taped tyvek and make it a no-money project.
I am interested to see what kind of solutions you come up with in your project. Frame packs are great fro carrying a big load, and provide great ventilation.
One thing they do is often put most of the load much higher, I suspect this is an advantage in tranferring more of the weight to the hips vertically, rather than pulling back on the straps when the load is lower.