In Marcello Minerbi’s book Alfa Romeo-Zagato SZ TZ, Giuseppe Busso talks about how the 750 Competizione came about: “This concept first developed through collaboration between Alfa Romeo and Abarth-Boano on a box-type sheet metal chassis conceived by Abarth. The car was built as a roadster and tested, but due to technical problems which came to light during the tests, Alfa gradually lost interest in it.”
Initially, the idea was to produce 50 cars, but as Busso points out technical problems haulted further development.
The car was powered by a long stroke Inline-4 that wasn’t too far off Alfa’s pre-war designs.
Eventually Alfa Romeo did produce the SZ as a purpose-built racecar, but this used a completely different philosophy, having Giulietta components in a tube-frame chassis.