The 47-55 panel body taillight is a distinctly different shape from a 56-59 panel body taillight. Most likely the license-plate lenses are different.
"They are oblong horizonaly with chrome trim . . "I think you will find that piece is stainless steel (the rear lens ring is chrome).
Here is a poor photo of the 47-55 panel body taillight housing. Sorry, but you cannot see the license lens on the bottom.
