Had the same problem with mine, as Brian says make sure that the cross bolt for the fork is out.
The other trick is to warm the cases, this releases the bearings and makes life easier.
I also found that the whole cluster has to come out in one piece, had to go back in that way too.
That’s when I discovered warming the cases —-
The other thing to check BEFORE reassembly are the draw-down bolts in the main case, these can have been over-tightened in the past, to replace them the box has to come out.
Now I know what it says in the book, just drop the tray and out it pops, well if your name is Paul Daniels it might —
It also makes sense to change the ball races unless you are absolutely sure they are good, it’s a cheap investment as is fitting lip seal upgrades.
Good luck, Mike