I am using a customized version of the responsive_classic template included in Zen Cart 1.5.5d and those files are no longer in the includes\templates\MY-CUSTOM-RESPONSIVE\templates folder as you suggested, however they are still there in the includes\templates\responsive_classic\templates folder. When I created my own template I used the override system and just copied all of the files from the responsive_classic template to my custom responsive template folder before making any modifications. Did I miss a step here?

Also, help me understand something please. When I use the template override system for my own custom responsive template am I still supposed to use the same override system in the template_default folders as well? I think this is where the confusion is coming into play.

By the way, thank you for all of your help so far in this matter.