Roger, yours is a familiar story.
My first Graphic a 2x3 Pacemaker Speed made in '47 had a spring (Graphic) back when I bought it. It now has a Pacemaker Graflok back that I took from a Miniature Speed Graphic; backs are fully interchangeable between Mini Speed and Pacemakers. Then I got a Century made in '52 with, of course, an integral Graflok to be able to use a 65/6.8 Raptar. And then two 2x3 Crowns, one made in '53, the other made later (the non-book doesn't contain its s/n), both with Grafloks. I bought one for its lens, the other as a parts camera and kept it as too good for that. There's no way to tell whether their Graflok backs were sold with the cameras or were retrofits.