force lower unit question

[oteps]

98 force 120. I am replacing the water pump impeller. Lower unit is off. I was going to shift it by hand but it is stuck in reverse? THe shaft moves a little over a half turn. Seems like the shaft on the motor moves about a spline width back and forth. THis motor has a splined shaft that turns not the one that moves up and down. Does it have to spin fast to shift into gear? My 175 merc wasn't like that.
History on motor. My father inlaw just purchased the boat. Ran 2 weekends but then shut off. My brotherinlaw "worked" on it. Had his buddy clean the carbs and put new plugs in. It ran on ear muffs but he said no water was coming out.
I should have ran it before I took the lower unit off but its an easy fix I didn't think about it then.