For what it's worth, the Culver City setup wasn't really and over-under deal; in the first picture you can make out the outer loop and where it exited and re-entered the oval. The elevation change was presumably to clear the wall, but also perhaps to help free the cars up to get around the right turns; see second picture of Troy-boy "freeing her up" big time.
Note also that the road-course loop is clearly abandoned; probably because it just didn't work out all that well.