Once I figured out how much of the gun had to come of it was no problem replicating the process on all of the guns. I simply removed the squared part, that fits into the turret, slapped a magnet on it and carefully fitted the shield on top of the part of the gun that sticks out from the turret.
I also fitted magnets to all of the guns. So the guns fits nice and tight against the turret.
To make the sponson-weapons and the hull-mounted weapon stick into place a fitted magnets into the bottom of the empty sockets and glued a peice of metal to the ends of the guns. It's not a really tight fit, but it keeps them in place much better than if you just leave them unglued.
I glued the sponsons in place, I could have magnetized them but I didn't want to have the whole tank go into peices if you picked it up from the table in the wrong way...

Since I'm playing a traitor-guard army this one will have the same kind of paintjob as the Vendetta and the Sentinel that are already in the army (pictures of the vendetta and the sentinel).
 
Now I just need to add some more metal to the  weapons and I'm ready for the painting!