more torque and power nissan 4x4

I got a GQ 4.2TD (1988) Nissan patrol 4x4 and use at work a new Nissan GU

4.2TD(2003) .theses two models use the same engine but the newer model has more torque and power figures GQ 4.2 TD torque 264Nm power 85Kw GU 4.2 TD torque 272Nm power 91Kw I am doing a engine rebuild on the older one and like to know what changes Nissan has made to get more power and torque out of the engine thanks anyone that can help P.S. I have thought about swapping engines