Apparently Automobili Lamborghini SpA decided to enter racing back in 1998, so they built this special Diablo GT2 featuring a modified engine pumping out over 600 Bhp and having a displacement of 6 Liter, some sources even stated this would be the engine for the Diablo successor but this turned out to be incorrect. This engine did however get used in the Diablo GT and Diablo VT 6.0 in more or less the same design, only slightly de-tuned for road use.
Personally I guess this car was a test bed for new technologies, but was not initially intended to be sold. The SV-R was a very competitive car and a new race car wasn't needed at that time, also the styling for the GT2 was surprisingly similar to those of the Swiss based Affolter tuned cars.
I did read somewhere that Affolter had designed a GT-car for Lamborghini, so it could be this Diablo GT2 evolution ?
The Diablo GT2 was actually on display at the Auto Show in Copenhagen in 1998, and it looked like Automobili Lamborghini SpA was trying to sell this redesigned Diablo, they even had a price for this special, $ 350,000, however during the 1999 Geneva Auto Show they showed the awesome Diablo GT, which was going to be the production unit. The Lamborghini Diablo GT went on sale starting in September of 1999, but only a limited production of 80 cars would be made.
Another rumor stated the new L147 engine would be used in this GT2 car to compete during the 24 hours of Le Mans in 1999, but that was just a rumor, and as far as I know there wasn't a Lamborghini entry in Le Mans for the notorious 24h race in 1999.