Every thing I have seen about the crate engines is the 300/320 HP unit is a tuck long block. Besides the unique cam and intake the 380/390 HP engines have higher compression pistons. Even Mopar Performance advertises that the 380/390 HP units have 10:1 compression pistons. They come with a 288/292 cam and a 9:1 compression wouldn't be enough to maintain reasonable cylinder pressure for acceptable low rpm torque.
The magnum crate motors are very good and can make a lot of power, they just aren't as good as the new hemi motors and within a few years they will be competitive price wise with the magnum motors.