Folks, Pietro, the OP, cited the revolving back feature of the (Mamiya) RZ as what he's trying to emulate - see his post #16. The cameras with "reversing" backs that have to be removed, flipped and remounted are not what he's after.
Off the top of my head, I can't think of a 4x5 with a revolving back that's going to be much shy of 6 pounds.
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