There are at least 4 cars related to this man:
1. a car he used to drive in some races and it was for sale not long ago (probably few knew who was its owner, since the car is standard)
2. a Fiat-based car, similar to this one.
3. a car he took to race after a radical conversion made by a Mr G. (not Giusti but more known) (former puzzle)
2b. an updated version of the Fiat-based car, already featured here, similar to this one (former puzzle)
4. the puzzle car, already mentioned here.
Car 2, 2b and 3 were tuned my Mr G.
The mistery builder is not Mr G.