If your talking about getting an original RB30T then you really dont have to change anything provided you obtain the computer but i would be changing the rear end and trying to source the Turbo rear axel and diff with disc brakes.
If your talking about bolting a turbo on to a RB30 then your talking about low compression pistons, higher flowing injectors re-built computer to the turbo specs turbo manifolds and thats not including everything else.