So I've just picked up 60 of these bad guys from Victoria miniatures link here:

http://victoriaminiatures.highwire.com/product/cthood-alien-heads

Bought them this morning, already been shipped - now that's service.  They match very nicely to the old school feeder tendrils heads of the standard GW genestealers.

I plan to put them on the catachan and squats to represent the hybrids.  My force will have mixtures of apparently unaugmented models, right through to the multi-limbed hybrids