Apex Modding has released an update (v0.92) for their GT3 mod. This new version comprises a new Camaro, BMW and Ferrari, in addition to the Mercedes Benz SLS AMG GT3, Corvette Z06, Porsche 997 GT3-R, and McLaren MP4-12C GT3 (which was added in the previous version of the mod).
Multiple liveries, from a variety of series, are included for each car. This mod is still a work in progress, but continues to be regularly updated, and has come on leaps and bounds since the initial release. The mod vastly improves upon the original that was released for rF1, and has been carefully adapted to be brought into rF2.
Apex Modding FIA GT3 0.92
FIA GT3 mod for rFactor 2, by Apex Modding