Since my customized fan bracket for Reflector's SuperMagnum fan duct failed, I decided to look into other options. The SuperMagnum duct itself is a sound design, but the centrifugal add-on as a separate piece leaves the blower fan without enough clearance. My solution was to redesign the main air box and integrate the fan mount directly into the duct.
I have not yet printed this design for testing, so use at your own risk, but it should work.
It uses the same 40mm centrifugal blower as the original SuperMagnum duct, but has a lip inside the air box for the fan to sit on, and mount for a single 3mm screw.
Obviously this is printed with the bracket opening pointed up, and supports turned touching buildplate only.
This is not the cleanest mod. I used Tinkercad to mod this, and so had a limited tool set. If it works out, I will try to clean it up in a real cad program at some point.