Does anyone know when Columbus started using red decals with SLX on the fork? I didn't think that happened until the early 90's but I could definitely be wrong.

I think I've seen a few Montellos with this kind of brake cable routing, but they're usually internal. As T-Mar says, the lack of chainstay bridge is the real indicator.

The flat fork crown on this bike looks like that on my ~1984 Gran Turismo (except that one is chrome). The later ones I've seen have a more sloping crown, at least in the upper models.