It is in fact a GT1 Evo, though it has been converted to be street legal.
Not to be confused with the factory street-legal GT1 Strabbenversions (sic), this car has a race history. It doesn't really say how or where it was certified for road use, but I imagine a large bag of small bills was involved.
1997 Porsche 911 GT1 Evolution | Monaco 2016 | RM Sotheby's
Lots of good reading at the Sothebys site, but here's the detail on the engine:
"600+ bhp, 3,164 cc air- and water-cooled horizontally opposed six-cylinder engine with two KKK turbochargers and Bosch electronic fuel injection, five-speed manual transmission"
