Where are the RPO codes located on a Delta 88 Royal. Are they located on the trunk sticker like on the Bonnevilles. Is there any other way of telling what my car has?

The two most common locations for ANY H Body was the spare tire cover (underside) or the deck lid (trunk lid underside). The only other way to gain the RPO information is to take your VIN to any GM Parts Department ask them nicely to provide with a RPO print out of that VIN.