Its possible. Did the first Gran Valley endurance just a few hours ago. Finished in 1 hr 24 minutes. Compared to my 1 hour 53 minutes in the Peugeot 908 lol
Its possible with B-Spec for a lot of races. I just found it in my used-dealership, an I've been leveling my B-Spec guy up REALLY quick now. You can use it in a few events in A-Spec as well (Like The Wind)