I've worked with these before, or something quite similar. We just packed dirt and/or sand under the light and ballast box until the top edge was even with the tops of the concrete forms. the light and ballast box had a white plastic temporary cover to hold back the concrete away from the top so the lid would fit down over the light and sit flush with the slab. It's also up the the concrete pourers to bring the concrete right up to the edges of the boxes evenly and not knock anything around. Hopefully you can supervise the pour. Hope it goes well.
