Too bad about the gloppy finish; hopefully it wasn't repainted due to damage/repair. If the finish is this bad, I'd hate to see the repair.

I think this is a relatively unmolested undrewed early 80s Mercier. They had some models that were built with Zeus bits (crowns and dropouts) around this time. They aren't very common (at least online) so I assume they weren't built for a long time.

The most common of these looked like the mystery frame here -- built with Super Vitus 971 tubing, Vitus dropouts and stock Zeus crowns (new style). They also originally sported the Shimano 600 drivetrain.
Most commonly the model name that's associated with these is "Lugano" although, more often than not, there is no mention of a model name when these show up in online listings or forums. I'm not a Mercier expert, so I don't know if Lugano was ever sold in the US - I assume this was a European market model. One BF member described the Lugano as "entry-level in their competition line at the time."

The serial numbers would have been on the head tube decal, so it's not surprising the owner can't locate one (not that it would be visible under all that powder).


Here are some comparisons -

Seat stay caps with the Mercier (M + crown) panto:





Fork crown/head lugs:





Dropouts, stay end treatment and the cable guide:





Underside of the bottom bracket shell: