I think that your best bet would be making a blueprint and layering sheets of wood (Kind of like 3d printing). Making it out of wood rather than foam will give it a sturdier feel, and more like if it was a real bomb. If you decide to go the wood route I would recommend a router to get all of the rough edges started, you would at least need a hand planer and jig saw. If you want the displays to work with your phone you would need to make an interactive app which is a pain (I know from experience). Have you considered printing out the displays and having a backlight? You could even have some tint to make it more realistic looking. If you are serious about this project I might be able to make some blueprints. Happy Building!