Because drifting puts a premium on controlling spinning rear tires and does not penalize for a slower lap time, reduced rear grip is the order of the day. Progress accomplished this by fitting 265/35-18 BFGs in the back, bolting on a slightly larger rear sway bar, and adding the aforementioned 4.10 rear gears.
The gears proved just right for drifting, and combined with the other changes, they allow the driver to finely adjust the rear grip with the throttle. The more throttle, the more sideways and slower the car goes; the less throttle, the straighter and faster the car goes. It's counterintuitive at first, but that's how it is in all crossed-up maneuvers when the rear tires are already spinning.