There's no serial number on the seat lug, so it should be on the bottom bracket, consist of two parts and be 1984 or more modern. The 600 components, if original, date it circa 1984-1987. Decal style can't be counted on, since it's a repaint.

I agree with the OP's mid-range assessment. The most common 600 equipped model during this period was the Limited. They were typically produced in Japan, though some production was pulled back to Italy after the yen evaluation circa 1985. It's probably Columbus Cromor or SL Tretubi.

Knowing the serial number would identify the year and then we may be able to figure out the model. The seat post diameter may provide clues as to the tubeset as would knowing if there are helical ridges in the bottom of the steering tube.