Shawn,
I was out of state, when I originally saw the post about the Rita Hayworth car and did not have any resources to check the chassis and engine number against.
Neither the chassis number nor engine number appear on my 1967 list entitled "Alfa Romeo Section of the V.S.C.C."
This is what is in the appendici of Alfa Romeo 6C 2500 by Angelo Tito Anselmi, p. 258:
Telaio numero: 915.871
Motore numero: 928.182
Appront. del telaio: 12.10.1949
Consegna vettura: 15.04.50
Carrozziere: Pinin Farina
Forma del Carrozzera: Cabriolet
C: -
Primo Acquirente: Goffredo Zehender, Milano
E: E
I hope some of this information is helpful in determining or tracking what car you actually have, keeping in mind that others have pointed out that the Anselmi book does have some errors or discrepancies, if I'm not mistaken. But it does show that the engine number and chassis number were originally built together and have not been changed, providing that no one has re-stamped to make them appear to match as original.
It appears from some of the recent comments that with the differences cited that two different cars may actually be confused, which will take some sorting out to be sure.
It appears to have been originally built or sold in December of 1949, but not to Kazan; it was sold in Milano instead of France. I have an issue with how a car could be produced or sold on approximately December 10, 1949, but appeared in a newsreel dated May 5, 1949, some 7 months or so earlier.
A little additional information from Guide to the Identification of Alfa Romeo Cars by Maurizio Tabucchi, p. 50:
"No significant modifications to the following models, except for variations to the bodywork:
...6C 2500 Super Sport (type 1947). Chassis from 915718 to 915890."
From Pininfarina Catalogue Raisonne, Volume 2, p.188:
The only thing I can find that matches the grill configuration shown in the picture that you linked to on your site is a 1949 Alfa Romeo 6C 2500 T Berlina; the grill configuration is identical as far as the small circles under the headlights and the unique angled cut to each side of the grill; however the hood and the rest of the car do not match. I cannot find a cabriolet with this grill configuration so it causes me to wonder...
Maybe someone with the Catalogue and better eye sight than I have can shed some light on the situation and identify the car and justify its status or authenticity.