I recently bought a 1956 Sierra wagon. I am having trouble identifying the trim line. It has chrome fenders and the Sierra brand on the rear fenders. Any ideas on how to tell if it's a Coronet, a Royal, a Custom or whatever?

 

Whoops! I just read my post and noticed that it refers to chrome fenders. Should read chrome fins! Based on online rseatch, I think I have a Custom Sierra wagon, but I also see references to a Royal Custom Sierra wagon and don't know what distinguishes the two. Any leads would be appreciated!