Here are two ways to break apart the fuselage, something I also had to do when I glued the fuselage of my F/A1-8 and forgot to add the cockpit.
One is to throw it into your freezer for an hour, the gentle squeeze down on the fuselage seams to crack apart.
And two is to use nail polish remover, use a Q-Tip dipped and just keep wiping along the seam, again gentle squeeze along fuselage seam to break apart.
It can be done with some patience and time.
Happy Modeling,
Joe