This is the base brackets to adapt the MK3 for the "Prusa i3 Adjustable Spool Holder." The rest of the spool holder can be found here:
The original brackets with that design did work ok, but the length of the arm on the front of the bracket would cause issues with the extruder carriage crashing during calibrating and printing near max high prints.
This allows the MK3 to print at max height and calibrate without the exturder carriage crashing into any of the brackets.
I also have a re-designed filament guide for the Mk3 available in my designs.
Printing with a brim might be a good idea. I generally print models 3-4 perimeters thick.