I suspect you may be right . . . if a prominent Simca site has no knowledge of this car, that raises a red flag for sure. I also find the following facts somewhat suspicious: As you pointed out, it looks like a ten-letter nameplate possibly starting with the letter "S" on the grille. Such as, perhaps, "Studebaker"? Interesting that the car has Studebaker Lark styling similarities, mainly the grille. Also, Studebaker did business over the years with Frua / Italsuisse, and the puzzle car could easily be attributed to them.
In SACO's defense, the puzzle car's picture IS identified on the Euro eBay website as a 1958 Simca Ariane. I suppose that until we find definitive information to refute that, the information we do have stands. I would love to find out for certain. And so the search continues . . . and don't we all just love a mystery?