I designed and printed this to fit into my friend's RC Stuka dive bomber. It is dual impeller set at Min third (5:6). The Impeller is printed in two parts and glued with CA. The unit is designed to use a standard 2212 brushless motor and ESC.
It uses a standard 5mm x 16mm bearing to stabilize the top end of the impeller.
Assemble the impeller,
Fit the motor to the mound and mount the impeller.
Push the motor assembly into the cage from the top.
Ensure that the impeller is turning freely and not touching the cage anywhere (may need some sanding and/or trimming).
Install the bearing and the cap, and adjust the position so that the impeller is not rubbing anywhere then lock the motor mount to the cage using thin CA.

Good luck.

Mine worked well but was touching in a few place and so some of the faces melted...but still works OK.