my '66 has a '73 12 bolt rear. it was originally a coil rear truck, so the leafs, mounts, and shackles from the donor truck had to come over too. i think the shock mounting on the frame had to be re-done, as well as relocated shock mounts on the 12 bolt.
i'm still working on getting the parking brake working, it was all pulled off as a v8350/th350 was added at the same time. i think i read elsewhere on the site that you need to pull over the entire brake cabling from the later model.
