Help Removing Lower Unit from Old Force Outboard (with video)

I bought an old (1987) 4hp Force outboard motor that I found on Craigslist. I plan to use it as a kicker motor on my 17' jon boat. I'm trying to remove the lower unit and I'm stuck - or it's stuck. I spent nearly 20 years as a maintenance mechanic working on all sorts of machinery so I'm pretty mechanically inclined but I'm stumped.

I've removed the bolts and disconnected the shift linkage. The unit is loose and wobbles freely but I can't get it to drop down. I think this unit was only used in fresh water as there is no corrosion or rust anywhere. So, I doubt that the problem is corroded or rusted shaft splines - but I can't see that so I can't be sure.

I could get a bigger hammer but I hate having to fix stuff that I broke. Any advice is appreciated.

https://youtu.be/o47PAoyagaA

Rusted splines it was. After you confirmed that I had disconnected everything that should be disconnected, I started hammering. I slightly bent the cavitation plate but banged it back into shape. I then made a too to give me a bigger area to hammer and the lower unit popped right off.

Thank you.

https://youtu.be/JB17UOWSbm0