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.
Very interesting! I bought it (slightly) used in 1979 and the dealer said it was one year old. The rear drop outs definitely measure 120 mm. Maybe it is older. There is a serial code stamped on the bottom of the bottom bracket. Any idea who can tell me what the numbers mean?