John, the problem has been diagnosed correctly. The OP has a roll holder made to attach to a Graflex (as in SLR back) and a camera with a Graflok back.

I just replicated it with a "23" Graflex -- so marked -- back and a 2x3 Crown Graphic that has a Graflok back.

The solution is to buy a "23" Graphic -- so marked -- roll holder or an RH-8 roll holder to fit a 2x3 Graphic. With patience, one can be bought through eBay for a reasonable price.