The two ebay listings you linked to in your original post will work correctly with no need for any custom machining. Of course, if you have access to a machine shop and you enjoy making your own parts, then yes, combining a Toyo 4x5 back with a Plaubel 5x7 rear plate will work too. There are threads on this forum for showing off custom-designed do-it-yourself cameras, many of which exhibit very advanced machining skills.
