The viewfinder is a detachable accessory. It is attached to a bracket that is fastened to the camera by two screws. You need to punch holes through the covering at the correct locations. AFAIK every Super and Super Speed Graphic has the mounting holes.
You use different masks for different focal lengths, and the finder has rudimentary parallax correction based on distance.
I don't know if the rangefinder has the same field of view as a 135mm lens. You could use the pull-up sports finder for framing.
Kevin