Have you disconnected the gear shift rod?
This is usually done by a clip under the power head.

stuck 05/09/03 07:46:26
It's a '79 Mercury 7.5hp long shaft outboard. I have two shop manuals
which cover a variety of models from this era. They both describe
removing the 2 or 3 obvious nuts and separating the lower unit to
service the impeller. It is really bound at the leading edge and I'm
afraid of breaking something by prying. Is there some other process
involved here? I have to remove the prop and shaft and remove the
pinion gear to free the drive shaft? It pries apart at the joint just
above the cavitation plate to about 2 inches from the leading edge so
it seems like the drive shaft is more towards the middle and already
free. Please send help. Thanks for your time. sol.