Insert and seat the Z motors into the Z motor holders.

Use 4 x M3x10 screws and 4 x M3 Washers to mount each motor in it's place.

Insert the blind L brackets to Z frame extrusions.

Attach M8x40 screws but do not fully tighten them.

While assembling multi point screw joints, it is better not to fully tighten any screws before others in order to ensure proper alignment. Tighten them in order like after slightly tightening M8 screws, tighten the L brackets and tighten the M8 screws again and final tighten the brackets after that.