Actually I think the mechanical gear advantage would be in favor of the pinion--however by the time you go to only one brake unit instead of two--then reduce the radius even more---you can't beat the oem stuff----

A good way to go IF a person wanted to do discs---Lincoln Versi?, Caddie ? or an Ford explorer conversion that did sell for only around $300 a few years ago---the Lincoln and Caddie calipers have parking brake locks internal for the disc where as the explorer takes special discs with the small drum for the parking brake---If I remember which is which--