1971 Florida era license plate

My plate for my 69 Dart is Green background with white lettering. And the county was always the county first. Mine is 3-XXXXX. The second was the cars weight class 3D, 3-,3W, 3WW. The 3 represented Hillsborough County. I'm old enough to be around when these were in use. Funny thing is during this time when you sold your car, the tag went with it to the new owner if in the same county.