Drop the pan and remove the 4 13mm headed bolts that hold the aluminum governor cover at the back of the trans behind the valve body. Governor will come down with that cover. Remove the snap ring at the end of the governor and swap gears. Reassemble. If it's a fresh build you'll probably be able to reuse the gaskets. Torque the gov cover bolts probably 15-18 ft lbs (going from memory) and I know the pan is best at 8 ft lbs. I can probably post some pics tomorrow if you need them.