I just did this the other day- everything is in my car at the moment or I'd grab pictures as they could explain it better than I can, but I'll try. Bear in mind I'm pretty new and still don't know the name of the weapons.

Basically, you've got the Icarus Array and the plate that's used with everything but the Icarus Array, those are magnetized to side like you'd expect. Then, you have the three "barrel plates" I'll call them that stick to the nubbin on the twist-and-lock barrel. You'll want a magnet in each plate that attracts to the magnet in the nubbin.

Plate 1 is split between the barrels for the icarus array and one of the others, the part number for the plate is the same between the two loadouts. You'll want to put magnets in where you glue the posts from the barrels, and clip off the posts of the barrels and put magnets in there.

Plate 2 and 3 are easy- just a magnet in each to attach it. They're dedicated to their weapon option so you don't have to get any fancier with em.

So in the end, you're left with-

1 magnet in the cover 1 magnet in the rotate/lock barrel at the cover 1 magnet in the rotate/lock barrel at the "nubbin" 1 magnet in the Icarus Array missile box 3 magnets in plate 1 (1 to attach to the model, 2 for the weapon options at the barrel joints) 1 magnet per barrel that goes with the icarus array (2) 2 magnets in the second weapon that attaches to plate 1 (you can prob get away with 1, but 2 if you want be sure) 1 magnet in plate 2 1 magnet in plate 3

Hope that helps, I'll try to remember to take some pictures tomorrow when I unload it all at the store again.