I had a nice chat with the owner of this recently (and very nicely) restored Roadrunner. He kept everything Roadrunner, but took some liberties, like the color was for Roadrunners but not available until 1970.
He also explained the the trim panel between the tail lights was an option, making it appear a bit more like a GTX. He noted that Roadrunner's panel was pressed bright metal piece and the GTX had a die-cast trun piece.
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to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
https://creativecommons.org/licenses/by/2.0CC BY 2.0 Creative Commons Attribution 2.0 truetrue