Hi, Robert ~
Without the 4.25" extension (I've never used the extension ~ I'm the second owner), the bellows extends to around 200mm. Without the extension, I've had no no problem focusing my 100mm / 180mm / 270mm lenses. With the extension, goes to something over 300mm.
Minimum bellows extension looks to be (sorry ~ shortest lens I've used is 100mm) about 60-65mm ~ using standard bellows, that would be with no movements at all ~ no bag bellows or a recessed lens board.
Hope this helps ~