Guys,
First - The Mazda was a tube framed car and not racing with a normal production chassis.
Second - It had used 3 rotors instead of the normal 2.
Third - It was not really a GT car, but more like a DTM car.

As for the weight added to the Spyder, it is as follows:
The ACO has decreased the weight of the LMP1 cars by 25 Kg's and increased the weight of LMP2 cars by 50Kg's (they really don't want the Spyders competing with the diesels.
IMSA (ALMS) has not been so radical , and they have maintained the minimum weigh of the LMP1 but increased the weight of the LMP2's by 25 Kg's.
The ACO has further reduced the fuel tank capacity of the LMP2 cars by 10 liters. (they want to make sure that the Spyders cant be competitive in any way, at Le Mans)