Do a search for "trapper nelson pack" lots of pics, patent diagrams and build info.
I own a half dozen of them in various sizes and ages. They are dirt cheap. No one will buy them. They are common here as they were made in vancouver.
I would buy not build.
I have used them extensively. They work BUT if you plan on carrying wieght and care about preserving your spine health I'd strongly (pun) urge you to get a big dollar modern pack like a Mystery Ranch.
A pack board shines as a light weight rig but if you want to pack moose quarters or carry a 10 day load it will hurt you. I love using a pack board with no bag to carry a tarp wrapped around lunch, a small pot, some extra clothes and a spotting scope. More then that though and your using up the limited life span of your most important gear, vertebrate and hig joints. :wink:
I have a 'cracked' one here that you could have for the shipping cost to use as a pattern or if you want a 'good' one I could part with a useable one in trade for a repro french trade knife or a .62 cal RB mold.