74-80, Mid February 74 the change was made, it was for production purpose, the pre change over Ramchargers , the doors were cut on the truck on the assembly line and then the window frame section was welded to the top before that top was placed on that Ramcharger. each of those tops were specific to the truck it originally came on, yes you could swap tops between these specific trucks but each truck had it's own "door " clearances hence the cause of a lot of the fitment issues that plague those pre change over tops tops today.