By gauge do you mean the one in the clock location, right of the tach? If yes and it has the little triangular key recess in the center, it is a gauge and only a gauge. It indicates boost pressure, but does not control it. The orange needle should move with the regular needle and sit at the highest pressure level reached, until reset with the key.
Anyhow, sounds like a fun car. Post some pics. Someone else can chime in with a guess on power.
86 Ruf'd and rebuilt (sold)