Good guess!
So, time to tell the story behind: Riva was one of the several involved (and cheated) in the ALCA Volpe adventure. They made the body of the few units produced before the company managers run away with the money.
After a long trial, the only reimbursement that was assigned to Mario Riva for his job was an uncomplete car, not in running-condition. However, this was in the eraly 50s, when the Volpe styling was rather old, and so he decided to modify (I don't know how) the mechanichs, install an engine to made it running and also to make a new body, with a more modern and attractive styling.