62 C20 Rear Bumper Question

[Soupsdad]

Help, brothers and sisters! I've got a 62 C20 longbed stepside. I've got a new repro rear bumper I want to install, but I'm having a hell of a time with the brackets. I don't have the originals. First round, ordered the wrong set (63-66) from LMC. Ordered another set from CI (because LMC didn't have a set for 60-62), but there's a label on the box that says they're for a half-ton. Phone support for Classic says they won't fit a 3/4 ton, frames aren't the same. What say you? I'd hate to return a second set! Thanks in advance for your help!