You do understand that the lens will cover nominal 6x6, not 2x3, don't you? And that the rangefinders fitted to 2x3 Graphics aren't quickly or easily adjusted.
I would want to get an RH-12 (6x6) or RH-10 (6x7) back - I don't really care for the 2x3 aspect ratio, I was just referring to the type of camera. As for the rangefinder, I read of people using 80mm Heliars and the like on their Graphics and using them as RF cameras, so the adjustment must be doable.
“For me, the camera is a sketch book, an instrument of intuition and spontaneity.”
― Henri Cartier-Bresson