47-53 definitely mount to the end side of the stake pocket.
IMG_5253 by
Joe Doh, on Flickr
54-55 taillights definitely mount to the fender side of the stake pocket. (these are 54-55 taillights, and I custom made the bracket with a license plate bracket)
IMG_6943 by
Joe Doh, on Flickr
IMG_6926 by
Joe Doh, on Flickr