I had a 1978 Cali Masi GC and it was 126mm. If yours is a 78 it won't be 120mm, I have owned lots of bikes and hardly any bike past '73 is 120mm.
Trek was making bikes with 120mm OLD up until 1981 or so. I have a box of 120mm Shimano hubs they tossed when marketing decided it was time to move to 126mm OLD.