Porsche should definitely use the same engine for the 997 GT3 as they use for the 997 GT3 Cup...
+ water cooled flat six-cylinder boxer engine
+ 3,598cc (stroke 76.4mm, bore 100mm diameter)
+ max. power: 294kW (400BHP) at 7,300rpm
+ max. torque: 400Nm at 6,500rpm
+ max. rpm: 8,200rpm
+ four valves per cylinder
+ water-cooled
+ dry-sump lubrication
+ two-stage resonance intake manifold, central inlet air duct
+ electronic engine management system MS 3.1
+ sequential multi-point fuel injection
+ fuel: 98 octane ROZ, unleaded
+ race exhaust system with lambda-probe-equipped catalytic converter
+ twin-branch centre exhaust pipes
The main attraction of the GT3 is that awesome engine!