Are you sure its a BB turbo? i have a spare t25 sitting at home and it looks much like that sept this turbo doesnt have an actuator which the t25 does But i think this turbo did originally come with a actuator cos you can see the connector arm hanging out at the bottom of flange on the exhaust side to the internal waste gate in the last picture.

There wasnt many stock garret BB turbo's that nissan used. s15 is the t28bb which this deff isnt.