I seem to recall that 135 was the alternate focal length for 4x5.
120 might be a bit short and vignett the corners.
That is unless the 120 is a 4x5 wide angle lens, designed to cover 4x5 film.
Do you have a vertical height limit that is driving you to want a shorter lens rather than just raising the head?
I my case, I cannot use the XL chassis because of a vertical height limit, which is the floor joists of the floor above.