Ford want to race it at Le Mans and engine size limit is something around 3.5 liters.
The engine size limitation for Le Mans went away last year.
http://www.autoblog.com/2012/06/17/le-mans-rule-changes-for-2014-announced-engine-restrictions-eas/
“The limitations of cylinders, restrictors and turbo pressures are removed.”
Before you get ideas of this turning into a Group B for Le Mans, the cars will be limited to an “energy allotment” per lap. A fuel meter will allow a diesel-powered car 3.99 liters per lap, a gas-powered car would get 4.95 liters per lap, from tanks that are about 12 percent smaller.
IIRC, the current Corvette racer ( C7R?) has a 5.5L engine and is legal for GT2. A 5.2L engine wouldn’t be a problem there.