The one shown has a 4x5 inch back. On which pretty much any Universal/Graflok type back can be mounted. Traditional 4x5 double dark slides, Grafmatics etc. and roll film backs up to 6x12 cm on 120. The 6x17 is a one format camera, also cm, also on 120. I didn't make the distinctions, but agree its a bit confusing when one all of a sudden switches from cm to inches without explanation. In general, Large Format sheet films are measured in inches, Medium Format on roll film in cm. There are exceptions.
A note on chopping up cameras. The making of my 4x5 was done without so much as touching anorher camera. The beauty of LF is that lenses, shutters, backs and all other important parts are just that: Parts, and can be bought piece by piece.