This car appears in Japanese version of Gran Turismo 3 A-Spec, despite back then polyphony doesn't really have a license to use Lamborghini in Gran Turismo. How?
Back then, this car run in JGTC, run by Japanese Lamborghini Owners Club. The car appeared using a licensing loophole, licensed from the constructor which ran the car in JGTC rather than Lamborghini. Due to risks of using this loophole, the car was hidden in the US version before being removed completely in the PAL versions. Lamborghinis officially appeared in Gran Turismo (PSP) but this particular car did not return until Gran Turismo 5.
This car also has a bit more power than the Standard Diablo, although some say the JGTC car produce well over 600hp.