I like my diff lock where it is under my left heel on L4610HST don't know where they put it on the GST. Real convenient for me as right foot is busy with HST pedal and once in a while the brakes which are on the right. Be careful about jamming the diff lock, if you forget, drive just briefly into better traction while in a turn it could really stress the drive gears in axle housing/diff.
I recall that hot rodders used to weld the diff to get super positraction and then their tires would screech and scrub in turns and if you turn sharp enough with good traction it broke axles or diff parts.
Patrick