The claw was made by cutting the axe and fingers off a Destroyer's right arm and pinning the claws from the Black Ivan kit instead. Hinges were added using small bits of plastic tubing, and it was cleaned up with greenstuff.
So how to store and transport these extra arms? Well, I've found that it's possible to use PP blisters and blister foam to hold them (I've got plenty of those lying around after all). I like to find three identical pieces of foam, cut custom pockets in one, then glue it to another using PVA. Add the third piece on top and lock it in the blister pack. It helps to write the contents on a piece of paper which I put inside, so I don't have to open every single pack to find the bit that I want. Also, you can fit two packs in a PP model/unit box to make transport easier.
I like how the claw turned out - in fact I think it looks better than the official one - but I don't like the angle that it sits on the Destroyer body, especially since it's a little hard to see which makes it less obvious that it's Black Ivan and not just a regular jack. Unfortunately there wasn't much I could do about that since the Destroyer was already painted, but I might add on Ivan's shoulder-spikes in the future. While the Kodiak arms on the Juggernaut body look a little too red to me, the pose looks pretty good so overall I'm happy. Now to see if he's any good on the tabletop.