I don't have faith the DP's will challange the first year they are together. I think your spot on on the GX Class
edit:
The United SportsCar Racing series will run a total of five classes. The Prototype (P) class will consist of Daytona Prototype, ALMS P2 and Delta Wing cars, while the Prototype Challenge (PC) class will consist of ALMS LMPC cars.
On the production side, the GT Le Mans (GTLM) class will be for ALMS GTE entrants, while the GT Daytona (GTD) class will consist of both Grand-Am GT and ALMS GTC entrants. Finally, the GX class, introduced for the 2013 Grand-Am season, will carry over into 2014.