I needed to upgrade my extruder to print TPU. The original had the usual problems (poorly constrained filament path). Referring to JamieBK's thing 4555065, Madeau3D's 3589452, and Joshvv's 2144277 I decided to combine the solid bodies of the mounting brackets with the extruder backplate, while tightening up the filament path with Joshvv's idea for the replaceable tube trimmed to fill the gap between the extruder drive gear and the backing plate. Because the motor mounting bracket is now the thickness of both the old bracket and the extruder (plus a little) strength is not an issue. I also added about 1.2mm to the flange thickness to make sure the motor mounting screws did not bottom out.

Print with supports as shown in the .stl file, making sure it is sitting flat on the build plate.