I found a set of early 80's F150 beams & arms with hubs and rotors for $250, apparently the beams are forged and more desirable. Seems reasonable, but after more reading, factory beam parts aren't strong for really beating on. But I don't know the limitations... if a Bonneville on 35's is too much for stock Ford parts...?
Then, I found this... https://www.diyoffroad.com/i-beam-suspension.html
You can buy the files to fabricate a completely custom beam suspension and have your favorite plasma table owner cut out your parts and DIY them! Looks like you can customize everything from the tabs to the frame crossmembers, beams, arms, swing steering, etc, etc. They even offer upright (knuckle) kits!
I'll have to take some measurements on the Bonneville and see. It would be bitchen to have custom fabbed beams on this car!