For normal (non-telephoto) LF lenses the focal length, say 250mm (roughly 10"), is also roughly the distance from the film plane to the lens board when focused at infinity. If you want to focus on something closer than infinity then the distance between film and lens board has to get longer.
To focus on something 20" (500mm) from the lens board with a 250mm lens the distance from lens board to film needs to be 20" (500mm) so your 22" (550mm) rail should work very nicely with a 250mm lens. A 300mm lens will probably work for most situations but the close focus point is going to be out a bit farther, a 500mm lens will just focus on considerably more distant subjects and be useless for close subjects, a 600mm lens would probably never find focus on your camera.
So much to learn about this large format stuff! Thanks for the info.