I'm guessing this will fit into the standard type 55 pola back for 5x4? If so, Paul, any 5x4 LF camera with a sprung back is the answer I think. Are the backs cheap? might be the time to snap one or two up for a profit?L.
If the New 55 comes to market with compatibility for the old 545 backs, you're bound to see them jump back to original price. In an old 2004 Calumet catalog I have, the 545 Pro back was going for 199.00 US$.
Bugger it. I've just checked and the Fuji stuff is a "pack" rather than single sheets.