Your registration date is...... not that helpful in narrowing down which style rear you have.
For instance I know of a Heerey that wasn't registered till 1982, but there wasnt any sold after 1972.
So here are some photographs which may help you.
Or you could post up a picture of your car.
Picture 1. Cox Gtm Rear endPicture 2. Heerey Gtm rear endPicture 3. Gtm Coupe rear end