Here is a vid' for you to watch. https://www.youtube.com/watch?v=O9xEi6ymTYQ
This young guy managed to complete the job the hard way. By watching, at least you can see what to expect to find when the gearcase has been separated from the mid section.
1. The Water Tube usually stays put (connected to the Block)
2. Eventually, he worked out that he should have reinstalled the Water Tube before trying to refit the gearcase.
3. That was the wrong way to install any outboard impeller.
a. Do NOT use any type of oil on any outboard impeller. Use plumbers "O" ring and washer silicone/lube.
b. Apply a dab grease to drive shaft recess for Impeller Key.
c. Install Key.
d. Slide Impeller down drive shaft and over Key.
e. Slide Pump Housing down drive shaft and let it sit gently on top of the Impeller.
f. Whilst rotating drive shaft slowly with one hand, press down on top of Pump Housing with the other hand until the Housing seats. Fit and tighten all nuts and screw.
g. Lubricate the rubber Slinger and slide it down all the way down the drive shaft, until it sits snugly on top of the Pump Housing.
h. Apply grease to drive shaft spline and shift shaft spline, as well as all the studs.
When refitting a gearcase, always remove all Spark Plugs so it's easier to slightly rotate the flywheel by hand thus enabling the crankshaft splines and the drive shaft splines to line up (mesh).
I always ensure the control box is in Neutral before removing the gearcase. When is Neutral there is virtually no easy movement possible, of the gearcase end of the shift shaft assembly. Thus making the entire refitting process of the gearcase, far less troublesome.