These are the standard sponson lascannons from a predator. I had two pairs of them left over after finishing a couple of blood angel baal predators. You simply take the left and right lascannon and remove the rivets on the sides without the skulls. Then its simply a matter of gluing them together.
My plan is to add magnets to the tops, and then place magnets within the valkyrie wings so that I can switch between missiles, rocket pods and lascannon. I already have the magnets, which I got from Hobby Lobby and they are strong enough to hold through plastic. I use this trick on my sponsons with my Leman Russes. I just need to wait until Saturday to get my Valkyrie, so I can see where the magnets need to go in the lascannons to make them mount correctly on the wings.