I know about confusion, which made me headache too for a very long time:
This may be the right solution:
Very first Formula Junior race in Italy, Monza 1958: 25/4/1958: 'II Trofeo Felice Bonetto' within the 'IV Trofeo Vigorelli'
Winner: Roberto Lippi, Stanguellini, ahead of Berardo Taraschi (race number 6, Taraschi FJ with bodywork as on the picture, you attached to your message)
Picture of the starting grid attached
Fourth round of the Italian Formula Junior Chamionship in 1958: 28-29/06/1958: 'I Junior Cup' (opener of the Monza 500-Mile race (Monza-Indianapolis)
The June race was held on the Monza-high-speed-track with banked turns, including a chicane on the main straight (like in April)
Winner: Nobile (Stanguellini) ahead of Lippi (Bardhal Stanguellini)
Berardo Taraschi's race car (the puzzle car) again wears race number #6 as in April.
Taraschi was forced out in the first lap, due to a multiple collision at the chicane. Gastone Zanarotti (Stanguelllini) and Adrien Bec (Bec) involved
Crash picture attached