I wouldn't even do the efford of mounting that motor cover/fan mount.
This will get the temps of the motor higher then normal.
Depending on motor type it's even better to mount a fan behind the motor, this is more effective to cool the motor then a fan above the motor.
But this depends on type of motor you are going to use.
If you are using a standard kit supplied silvercan mabuchi motor it's better to cool the motor on top of it, but when using a silvercan johnson motor then it's more efficient to cool the motor from behind.
Cause the fan is able to blow directly into the motor wich keeps the motor cooler.
When building the car make sure you have a set of 5mm shims to use for the the suspension arms (lower&upper) and for the wheel axles to remove some slop.
And make sure you mount the carton motor plate between the motor and motormount, especially for endurance racing.