If the gap is larger at any point, the engine's motor mounts will have to be adjusted. When you view the couplings from aft facing forward, if an excessive gap existed at the 3-o'clock position, then the front of the engine would have to be moved to starboard. If a gap existed at the 6-o'clock position, the front of the engine would have to be lowered. Once the gap size is acceptable, rotate the shaft coupling 180 degrees and recheck the measurements. If any change has occurred, then the coupling, the shaft, or the fit between the two isn't true; in such a case, they'll then need to be removed and taken to a shaft shop for inspection, fitting, and facing.