If the gearbox has a mid belt shield , remove it.
Make sure no cables are connected to the gearbox. Remove the gearbox from the machine.
Remove (5) of the (6) bolts from the gearbox assembly. Do not remove (1) of the bolts near the rear of the machine. Loosen this (1) remaining bolt. With your hands, pull the gearbox toward the spindle. This loosens the tension on the spindle belt . Connect the hoist to the gearbox . Lift the hoist until it supports the gearbox. Remove the (1) remaining bolt from the gearbox assembly. Slowly lift the gearbox.
Remove the gearbox from the machine. Move the transmission oil pump assembly  and the spindle encoder  to the new gearbox.