As a data point, I pulled out the Petter 7HP diesel out of my Catalina 27 using the boom and a block and tackle I rigged from the boom vang and something else that I had lying around.
I'm guessing the engine weighed about 250 lbs (huge flywheel!)
I transferred it to a skid in the cockpit, shifted the block and tackle aft, and swung the engine onto a furniture dolly, which I rolled up the dock.
It came out pretty easily. Of course, you don't want to drop it, as it could seriously hurt you and your boat.
I replaced the engine with a Universal M2-12 (175lbs) without much difficulty.
You could reduce the weight significantly by pulling the transmission and accessories before you lift it.
I would certainly, carefully do this again if I needed to.
I would expect that others will chime in shortly with other, possibly better advice.
1987 CS 36 Merlin "Kyrie"
"They drove a dump truck full of money up to my house. I'm not made of stone!" -Krusty the Clown