I'd think the fronts would be easy. The Wilwood kit is designed for a 2011 Fiesta and fits the Fiesta ST. So wouldn't it stand to reason that the ST brakes would fit the base Fiesta?I would guess that the ST front brakes are probably an easy swap. The rear disks will be more complex if only because of the ABS.
Its a shame that Ford didn't make rear disks standard on the base model.