The third try to get an acceptable head is sadly not my own idea - though it will change from the original, it's an idea I have nicked from Dave Taylor, luckily with permission. It looked so good I instantly knew I might end up using it for these guys. Check out his extremely cool AdMech HERE - scroll down for the biomostrosities.
Anyway the head will consist of a head/helmet from the DA talos painengine, over an WHFB orc head. Various bits of metal, cables and such will of cause be added. I've made a mockup shown below, and I think  that it fits sizewise. The Ogryn head is still looks way too large even though I tried to use as little bluetac as possible so it wouldn't cloud the picture. I think the DA mask will be lowered a bit on the body, to give a slightly more lumbering look.