I, like many many others, was not going to field my killa kans with mixed weaponry, and after deciding on my army list I decided to get creative and make 9 kans with rokkit arms.
The pictures provided use red to show where I've cut and I've tried to label where the different parts are from. This tutorial assumes you have a working knowledge of the killa kan box set.
Here are my conversions:
1) This is the first one I came up with:
I noticed that the rokkit launcha and big shoota arms included in the Kans box set are separated similarly: there is an arm with a top piece that needs to be attached. By swapping the top pieces on the arms (and cutting them away to fit) I was able to make the big shoota into a rokkit launcha! As mentioned before, I took the top part from the rokkit arm and fit it on the big shoota base, chopped the little gauge gubbin off the rokkit arm and fit it in the top part on the big shoota arm. To give it another rokkit (I wanted them all to have at least 2) I cut off the screw on the ammo drum and attached a rokkit cut off of a rokkit launcha boy.
2) Then, I used the left over rokkit/big shoot arm to make this:
I simply attached the big shoota gun part to the rokkit launcha arm, cut off the barrel and glued one of those random spikes from the deff dread kit to cover up the bare spot. This one's not my favorite (the top still looks like a gun), but it gets the job done.
3) I used left over Deff Dread bits to make this one:
This one involved the most cutting to fit the rokkits on the arm. I took the grotzooka arm from the killa kans and cut off the stick. Then I took the ball for the dread socket and cut it flat so it could lay flush against the grotzooka arm (see the inset pic above). Then I cut the back of the rokkit attachment so
it would lay flat and glued it all together (I glued the ball on the rokkit attachment, as usual, first. Then I glued that onto the amputated grotzooka arm). It looked a little weedy so I added some wire for good measure.
4) My favorite

:
I took that piston-driven-looking killa kan close combat arm, clipped off the back rods, cut off the front socket for a
ccw and glued on two rokkits (from ork boyz and lootas/burnas). I added some wires, as you can see, to make use of the leftoever pistony things and viola!
Here are the finished products:
I hope this helps you make your own! Let me know what you think!!