Since the cable shown above as available (the 395 one) fits our box at the box-end, which it must, then if the only problem is the length to the quadant, you could shorten inner and outer to fit. Don't quote me, but I think the quadrant end of the MGR cable is a plain cable with clamp for the outer and a kind if screw cable-nipple, you see. Will TRY and check that.
David