Again in response to m smith and the originality of a conv. back window. The date of manufacturer for the rear window ( and a very good indicator of the date of the top as well) can be found stamped in the lower corner of the window itself. Federal law mandated that this be done so there should be no exceptions. Normally, the window did not last as long as the tops and on occasion one will find an original top with a replacement window, but over the years I do not remember seeing an original window with a replacement top. Check out your window and maybe that will help in your determination of originality. I hope that others will join in this discussion and post some images of what an original rear window date stamp looks like - probably few of us have had the pleasure of a good look at this part of Mustang history.