Does anyone know how long the 78Js will be on the EWR-LAX route for?

I ask because we are looking to book a OW LAX-EWR in late August. We would really like to try the 78J on the 9:15pm departure, UA1882. The problem is we will be making a few other sacrafices on our trip to be able to get on this particular flight and I would really hate to book this flight and have an equipment change before August. The following thoughts come to mind:

1. This flight is 7 months out and a lot can change between now and then.
2. While new aircraft fly domestic for the first couple of months, I would imaging the bugs would be out of them by August and they will all be in international service by then.
3. Even if there is a schedule change if they swap the equipment, I feel I would have a hard time convincing an agent to move us to the flight that works the best for us time wise, the 12:15am departure, since we would not be switching to another 78J.
4. Fear that it would be swapped to the domestic 777, the new ghetto-bird, which I really do not want to fly in for our first flight in 3 years. (Note: I don't mind the 752s and while not perfectly ideal, I could live with the 9:15pm departure as a 752 if I had to).