I pulled the rear seat out of my other 74 Charger and the divider is not insulated and it does not have the insulation covering the wheel wells. I did find the broadcast sheet for a 73 WP Charger with M code engine under the seat though. I suspect the interior was changed out because it does not have the 74 seat front seat belts and it has a front bench seat with armrest. Sorry I could not help you 340Cpe. I will be insulating my trunk divider also and will be facing it toward the seat back.
Terry