Arch,
Unfortunately, the 116520's 4130 has the same size pinions as the EP400; as such, fitting a gen 116520 dial on a 7750 based movement is a no-go since the 7750's pinions are significantly larger (i.e. the dial's opening is too small).
Additionally, the gen case is far too slim to fit the modified 7750 for seconds at 6:00; the thin case rep is only doable since there's a large flange on the backside of the case to facilitate the extra height of the movement.