yes a boost gauge is useful, just connect it to the smaller of the two vacuum/boost pipes that are coming of the back of the plenum chamber by the throttle body. the larger one is vacuum assist for the brake servro the pipe for that has a one way valve inside the pipe don't bin this pipe and replace it, unless you replce the one way valve in the new pipe. the smaller pipe goes to the front of the car and down to the recirc vent valve for the turbo. put the T piece in this pipe and run it to the gauge. don't use the pipe coming off the front of the throttle body as this goes to the fuel pressure regulator solenoid and you don't want to disrupt this vac/pressure.
just thought i would pass this on to you