I do not have the Nardi book so I have pieced together what I have found, with some gaps.
Chassis no. 948-4 was built by Nardi-Danese as part of a small run of cars powered by Alfa Romeo 6c 2500 engines and destined for the Mille Miglia. This one was built for Ermanno Gurgo Salio with a spyder body and entered in the 1948 race.
The following year it acquired a Motto coupe body and again raced - with little success.
Around 1950 the car was imported into the USA. I have a photo of it surrounded by those responsible, including Tony Pompeo who was to gain fame for importing and racing numerous Ferraris.
However this car did not keep its Alfa engine for long, because it was next seen with a 6 cylinder GMC (truck) engine fitted with Wayne Speed equipment. Wayne may have done the conversion, and there are numerous photos of it being raced (and crashed) by Bill Kerrigan.
The trail goes cold in about 1956, and the car has since disappeared, but in it's later years of racing it was described as a Nardi - Chevrolet, again fiitted with Wayne speed equipment. Whether this was another engine transplant or an error I have not been able to establish.