Make sure that the pump's brusholder is in the correct position, like in the first picture. You should have the cables looking down on the right and the MARCO logo in the sticker on the stator that looks toward pump's head.

Insert the pump's head tie-rods in the holes between the magnets.

There's only one way to mount it right, the other is upside down! Watch the pictures.

Push the tie-rods down to the end of the motor: they should come out on the other side, as seen in the next steps.

The smaller motors have the tie-rods placed horizontally: refer to the position of the holes in the pump's head to understand the right direction to assembly them!