That bike appears to have 1.) a Vitus frame - but not fork, 2.) Huret dropouts, 3.) Bocama Lugs, 4.) braze-on derailleur cable guides on the BB. These are on the 79 grand touring...
BUT, that year/model also shows braze-on brake cable guides, and also different paint.

My 76 catalog shows the Grand Touring as the only model with Vitus tubing, bocama lugs, Motobecane fork, clamp-on cable brake cable guides... but with generic Motobecane forged dropouts and fork tips and the older pattern paint, and also a different headbadge - on ALL the bikes.

One good indication would be when they may have started using a headtube decal with a simple "M" - the 76 and earlier bikes had the riveted metal oval headbadge.

So, I'd go for one of the 77-78 models.