These were a GMC item so I've been told, but they fit Chevy just the same. That's my red 46 btw and I copied an original set in stainless, easy deal. I have seen a NOS set 'GM' had all the instructions, so they were available but not many truck owners wanted to shell out the extra $1.25 at the time so they can be hard to find. There are several aftermarket props used on lots of Ford street rods that are being reproduced.

It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed