I've located a goodly stash of tyranid bits, and the smaller termagant arms make great fodder for hybrid arm conversions. You can see one on the 2nd generation here, with the missing hand. I may swap the mask on his back for a purestrain servo skull. He's shaping up to be a squad leader, I'm thinking.
A package of good stuff from Victoria Miniatures provided these resin arms and alien (Cthood) heads. I think they make great early generation hybrid heads, particularly from Ymgarl variant purestrains. They work with the Games Workshop ghoul bodies very well indeed. A little warm water bending will be required for the arms to fit, which were a little roughly cast, getting them off the gate in one piece will be a chore, for example. Great parts for all that though. The bases are from Dragonforge. My basing will be wrecked urban, so these do the job nicely.
Another welcome item from Dragonforge are these poseable metal cables. You can't have infected adeptus mechanicus without some cabling attaching various bits to other bits. I did consider guitar string, but the fact these can be bent to the required shape is a winner for me.
All very exciting. Once the ettin is wrapped I may dive in and start building hybrid squad one. I've recently amassed enough original hybrids for another squad, problem now is making the originals and converted ones look like they are from a coherent force.