Additional info. You can do all the work described earlier with the boat in the water. You won't have a lot of room 2-3" max to move the shaft aft to remove the shaft coupler from the shaft. Also, all nuts and bolts are metric. Don't know the size of the keyway- again, probably metric.
There is one thing that may keep you from doing the work with the boat in the water. If there is a sacrificial zinc mounted in front of the strut it may prohibit you from moving the shaft far enough aft to remove the coupler.
Worse case, if you can not slide the shaft back to get the coupler off the shaft, Perhaps you can get a short key into the coupler/shaft.
Then tighten the two square head screws, lock them with the nuts, Wire the two square nuts, align the engine to the shaft and deal with it at the end of the season or in the spring.
Next spring, think about re stuffing the stuffing box and checking the cutlass bearing
