The key is tapered and driven in.
We've discussed this in the past on this board many times before.
My suggestion is to pull out the key and then the flywheel should slide right off. Drill and tap the key, then use some sort of slide hammer arrangement to pull the key out. This should work well if everything is not rusted solid.
After I took my #5 apart the hard why, then I discovered the tapered key. The key is the only thing that holds the flywheel on.
Otherwise the puller idea may work if the key comes with the flywheel.