I've replaced a lower unit on my old 27 without a problem about 2 years ago. Now I'm trying to do it on a 36, which should be the same but a bit heavier. I've tried everything and I have to be missing something.
Removed the four bolts/spacers and the motor aint budging.

I'm in the middle of doing the same thing but on a 32. Replaced it a few years ago and had no problems. Now this one is stuck good.

Rather than keep fighting it in my garage with pry bars and hammers and trying to lift it using a comealong, I think I'm going to try and make some jacking nuts using some all thread and nuts and take it to my work and use the overhead crane to lift it.

Has anyone made up some jacking nuts and if so did they work?

Okay, finally got the sum beach off Friday night...took it to my shop and used the overhead crane and a couple of pry bars. Didn't want to budge so I sprayed some penetrating fluid into one of the holes in the collar (i think it got down in there) and it still wouldn't budge. Ended up using a couple of small steel wedges under the pry bar and wouldn't you know it, it finally came apart...

Put plenty of neverseize on it when you put it back together

IMO you should get to know the ins and outs of general maint on any of these things. As rough as we are on them it makes sense. I have come to the conclusion that it is a good idea to pull your LU once a year just to ensure these things dont freeze up and to get a good look inside. The grease can get gummy over time and you can make sure fresh grease is getting into every nook and cranny that it needs to. Including adding fresh anti-seize to nuts and bolts and other things. I can have this done in about an hour on my PD.