How difficult should it be to turn over by hand??

Once the piston/ring assemblies are in, yes it gets harder. Those cast rings put a lot of drag on the cylinder walls. And you are right; the break-away torque is quite a bit more than the turning torque after break-away. If you were paying attention during the piston install, you would have noticed the incremental increase as each next piston went in.
check also post 2.