Does a 545 Polaroid back fit on an Anniversary with a standard Graphic back?

Yes, it does. Like its predecessor, the "500," and its modern variants, it is little (if any) thicker than a conventional double-sided sheetfilm holder, and so it slides smoothly under the spring-loaded focusing panel.

What will not fit are the "450" (for the commonly-available 3¼x4¼ filmpacks) and the "550" (for the increasingly hard-to-find 4x5 filmpacks).