The problem I see with your layout is that there is not enough room for the trestle to go up on one side and then down on the other side of the layout. Would you consider just one track going up and then have a reverse loop for the return? I have attached a picture to show how it might work. I assumed that the elevated part is not mainline so I could use O36 track and I elevated a section of the mainline over a hump around the railyard so there could be a higher elevation to start the trestle. I have shown all elevated track in red.
