The 197mm is actually 197mm square. You got me excited there for a second--I am planning to modify a B&J and build a 5x7 back for a Kodak Master View 8x10, so I looked at the 4x5 again--much lighter if it would work. However, the way the bellows mounts through the back of the Wisner and is held in by the film pack/focus panel, the bellows back limits the exposure field to about 6 inches in each direction so that the back can be rotated 90 degrees. I can manage that much wood working, but not much more.
Now you have me thinking--it looks like it needs about a 1" extension. The Wisner body is only 1/4" thick and even thinner where the wood is mortised to hold the bellows, and I don't really want to modify the body itself, but maybe an extension that fits over the outside dimension of the box... I'd have to sharpen my wood working skills and figure out how to attaché the 5x7 back to the body. I still want the 90 degree rotation.