My initial vision is something like a larger Hive Guard. Four limbs, and then the gun arms. I'm pondering an over-and-under kind of weapon, since the Rupture Cannon is apparently a two-stage weapon (first the tick that pops and coats the target with jell, then the second shot that detonates it). But, first, we have to have the bracing arms.
This is step one of the process. They're kind enough to give me three carapace-tops for the 'fex. I used the one with the little pointy spines (since I'll be giving the Tyrannofex Cluster Spines without fail), and butchered the smooth one and the spore cyst one.
And now, a use for the crushing claws. I mean, it's not like we'd equip the carnifex with them. You can see on the right where it's a pretty clean cut between the claw and the wrist, and then chop the lower claw off. Then, it's a matter of glue and patience.
And now, the finished forelimbs. In lieu of using green stuff all the way through, I build it up with layers of hot glue. Hey, it's a lot cheaper than greenstuff, and sets faster. Then, it's two layers of green stuff; one for the details on the side, and a seperate application of the scale-top bits.
And now, a showcase of my terrible photography. I took a few shots of the modifications to the torso and waist. In order to make the thing taller, I severed the 'fex waist/tail, and reversed it. Instead of having a hunched S-curve to it, the model stands a little taller. Note that you'll have to remove some bits to make the torso fit.
The Grey Knight has graciously volunteered to hold up the curing torso/leg joint. I intend to offer updates as I work, and better pictures than the last one. Had to get the girlfriend to take the completed forelimb pics; I was just having a case of the Fail there.