So most ~80's Pinarellos have 'Treviso' on the seat tube, but this isn't an indication of model, it's just where they were made.

However, there was a Treviso model. See if you can make out any ghost decals on the top tube near the head tube end.

Typically a Treviso wouldn't have internal cable routing, but they do pop up from time to time. Also, a Treviso would typically have a chainstay bridge, but I think they started to lose them as the 80's wound up.

The Pinarello stamped dropouts and fork tips, along with the BB shell suggest post '87, I'd even go as far as saying '89.

The serial number doesn't really fit the known formats, so I'm wondering if this is a custom job of some description. The BB shell suggests a Gavia or Veneto model (I think) but other details don't support that.

See if there are any internal helical reinforcements to the bottom of the seat tube - this would indicate SLX tubing.

I don't think it's a Montello because there entire rear triangle would typically be chrome, but like everything Pinarello, there are always exceptions.

Might need to do some more research on this one...

Edit: even the brake bridge is giving me a headache - I can't find a model that used that type!

The shape of the missing paint on the head tube suggests the 'old' badge/decal, but by 1989 I thought it would be the stripy decal. Aaaargh!