yeah that could be pretty cool...it would take a fair bit of chopping and gluing, maybe some greenstuff, though that'd be optional...I'd say a good place to start would be to go to ebay and get yourself either some burning of prospero MKIII marines, or some dark imperium plague marines for a decent price (in case it all goes a bit wrong, might not want to go full-price on the models)...and I think a box of Crypt Ghouls (
CA$50 for 20 model's worth of bits -
link ) could probably get pretty close to that pic...chop a leg off a marine, then chop the leg in half at the knee, then do the same with a ghoul, and stick the ghoul thigh in between the marine hip and shin...do similar things with arms, swap out a head here and there...just have a good ol' play around