It's the oil tank for the drysump. He made a couple changes on the suspension one outing and it carried the front short-shifting into 3rd and when he lifted it 'tickled' the pan. End of season/year so I talked him into piecing together a used drysump system. He wanted to put a vacuum pump on it and it needed a new pan either way so the cost difference wasn't deterring. (Picks up major ground clearance too!)