Ferraris made 1743 308GTSi cars, over the period 1980, 1981 and 1982. The chassis numbers started at 31327 and should, therefore, have finished at 33070. I think the last element of the VIN is the chassis number which, at 35715 seems too high for a genuine 308GTSi. Mind you I could be wrong about the last part of the VIN number identifying the chassis.
Ken.