I copied the dimensions of the original injection molded part, but changed the design to a tie mount instead of a screw mount which cracked frequently even with the OEM molded replacements. I made some flexible TPU re-usable cable ties to secure the screen mount from https://www.printables.com/model/124743-tpu-flex-cable-zip-tie. These held the screen in place very well while exercising. 

This can print on it's side without supports from Bambu Studio just fine. You might need to print with supports if bridging is not supported in your slicer. 

Printed using 0.2 mm layer height, 5 wall layers, 50% infill.