Race hard tyres, pitstops in lap 34 and 68.
Tunes: https://sites.google.com/site/gt5tune/nascar
Herbies tune is pretty good if I remember right. Perhaps minor tweaking for endurance needed.
Correct Dr, thats the hot lap tune, can go pretty far but not great for Racing Hards. At least for me the car can get loose fast. Downforce, toe and camber really are the things you'll need to change for endurance racing.