This time I think the solution is pretty easy.
I do not know the article Pal found and I can't say anything about it but I wonder if it's an online article started by that picture.
The plate says Riva, but not only: that is actually Riva's logo. It means 1. It was built by Riva (the shipyard), or 2. Someone put there their logo there.
That logo can be seen just in that picture and then it was removed for good.
The info available from the seller's website (and not only) are full of details and honestly I can't see why they should made up it was designed by Muffato Nereu de Oliveira for Mario Borella to cover the involvement of a prestigious firm like Riva...