I think the only 'official' depiction of a Stalker is on the cover of Scrivener's Moon, so I've always seen Shrike as that but much more battered and falling apart. A bit Borg, a bit Terminator endoskeleton, a bit Frankenstein's Monster.
A lot of the cast seems fairly unknown, but then again, so were a lot of the
LotR cast at first. Jackson clearly has an eye for working with less well known actors and getting the best out of them.