Looking at the top of the drive, there should be a snap ring around the shaft thatsticks out of the top gear.
#1 in the attached diagram.
Once the snap ring is removed, that should allow you to lift the top drive gear,
#2, off of the shaft.
There should be a cross pin through the shaft. Slid that pin out, and the drive should drop away
from gear
#4, and out of the bottom of the boat.