I saw no real difference in the ones made in the eighties until the end of the run in the 90's. Then I saw some that had the franklin type design, but looked like from the outside like the older ones. Was also interesting to me that in the very beginning in the 60's, they had a full front that could be removed for service. That changed fairly quickly to the rear access panel. Never understood why they did that. It would have been MUCH easier to service from the front.