As far as I know 'Graphic' and 'Graflex' backs are two different things. A Graphic back would be the one on pre-graflok Speed/Crown Graphics, whereas the Graflex SLRs came equipped with the Graflex back. I *think* the 545 holder fits into the Graphic spring back, but not on the Graflex back.

That said, I don't think they make film for the 545 holders anymore.