You have Polara tail lights. The Monaco 500 had "MONACO" spelled out on the back, and it had the short piece of trim under the letters. Regular Canadian Monaco's, and all US/Canadian Polara's, had DODGE letters on the trunk, and no short piece of trim.
I highly doubt that your tail lights are the original lights for your car. If your front grill does not have a horizontal bar in the center, then it's a Polara center.
UNLESS - all convertibles had MONACO spelled out on the back, regardless if the car was a 500 or not?