The internal cable routing for the rear brake has me thinking Montello rather than Treviso. Pinarello didn't make things easy by naming a model after their home town: the Treviso name is cast into most of their bottom bracket shells, irrespective of model!
All the Trevisos I've seen had cable guides on the top tube and were made in Columbus SL, while Montellos were internally-routed and made from SLX. It looks from the photos like there's no bridge between the chainstays which would also indicate Montello/SLX rather than Treviso. All Trevisos had a bridge, no Montellos did. These are good things, as the Montello was a step up and a very classy bike indeed.
Pinarello decals from the 80s are notoriously terrible, so don't be put off by their condition or absence (Though it would be nice if there were more of the Columbus decal on the downtube... can you get a close-up?) If anything, them not being there implies the bike's not been messed around with or badly refurbished.
If you fancy getting gynaelogical, another way to check is to strip the bottom bracket and have a feel around for ridges or splines in the seat tube. These would confirm Columbs SLX tubing and therefore a Montello.
Good luck! Keep us posted
