It is difficult to obtain an accurate history of a lot of these cars but I have a slightly different scenario for 0050, 0308M, 0328M. After the factory had used 0308M for the protoype series of the Mondial and then 750 Monza the car was sold to Barbara Hutton (ie Rubirosa). Sequentially it was given to Rubirosa for his birthday. Serial number 0050 (already owned by Rubirosa) was renumbered to 0328M. Serial number 0328M was then renumbered to 0308M That left it open to renumber #0308M to 0050M to avoid tax taking the car back to France. It left Rubirosa owning two of the cars. No doubt there will be a difference of opinion to the above.
The scenario for the prototype Mondial series is certainly a can of worms best not opened in this thread. Its chassis number is certainly disputed but I think the racing history of the prototype, at least from its first appearance at Casablanca, is well established up to 1955. This is because it has some unique and easily identifiable visual features. Ownership is not so well documented but there is no indication that it was sold to Barbara Hutton or found its way to Rubirosa. If any one wants to start a new thread on this car I would be fascinated to see what comes up. Barchetta seems to think 0308M, originally a Vignale Berlinetta and not a prototype Mondial, was renumbered to 0050M and its history does not include ownership by Rubirosa.
I doubt Rubirosa bought any of his cars, with his own money. He married into a very high class society. Or put another way - he was a playboy.
Don't know if I would be that harsh Bira, to call him a gigolo. The guy was cool, hell he still has his name associated with pepper grinders in France. As far as the story about 0308M/0050M goes, it was told to me by an Italian who knew the car from the days he was working with Scagliettti . I don't think it was in Rubirosa's hands very long, but I have no reason not to believe him.
Rubirosa owned the car originally numbered 0328M. The Mondial protoype was built using 0308M. It seems not to have been raced before sold to Dan Collins in Denver, Colorado.