Are you sure it slides under the GG on some? That looks way too fat. I have a Calumet back for similar use and it is only about 1/2 inch thick for the purpose of replacing a 4x5 holder. Just asking for others who might be considering this. GLWS, Bob.
I have read that it will slide under many Toyo GGs, they have slightly more clearance.
It almost fit under my Linhof's, just a few more millimetres would have done it, but I didn't want to force it.
Thanks for the query.