On my 46, I mounted the plate dead center of the rear bumper supported and surrounded by a 49 Chev passenger front plate guard. You can buy these reproduced all over the place. I just got tired of catching my jeans on the plate sticking out the side of the bed and bending the plate. I can take a photo if you like.

You can just see the back end posted over at inliners.org bottom of home page click on Lodi picnic pics and look for the line up of 41-46 trucks, mine is 2nd red truck from the end.

Another thing I did prior to relocating the plate is that I made an aluminum backing for the plate using 1/8" plate. This helped a bit but then bent the whole affair when I caught the on thing.

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