The bellows extension has less to do with the lens choice and is more to do with the actual design of the camera. You need to decide whether the camera is to be double or triple extension, that's compared to a standard lens for the format. Double extension allows 1:1 focus with a standard lens.
Typically a 10x8 camera with a 300mm/12" lens has an extension of approx 24"-27" and a triple extension version around 36". Scale that up for your 14x11 camera and 36" may well be practical without the hassle of adding an additional extension rail.