On most current production 120 backing there's no room for a 6x7 track without potential confusion with the 6x6, 6x9, or 6x4.5 tracks. Better to keep your 6x9 camera in its native format and stick to those with frame counters for 6x7. I shoot 6x7 regularly on my Century Graphic -- because my RB67 film backs (and my Graflex RH20) fit its 2x3 Graflok mount. I also shoot 6x9 (Graflex 23), 6x6 (Graflex 22) and 6x4.5 (RB67 back natively in that format).