Guess that's all I can do at this point. I don't know much about motors, especially outboards, but it all looks pretty strait forward. Yet here I am. I will give it another try. Maybe I will get lucky and adding more water in the drum will work.
In post number 13 you said the impeller was sticking out of the housing a little bit while he was screwing the housing down. The impeller has to be bent into the bottom of the pump before securing the housing. With the key in place turn the driveshaft clockwise while pushing down on the housing to get the impeller seated.