Predators aren't all that concerned with blending in with human society (why blend in when you can cloak yourself?), but if one was looking for a bit of the steampunk aesthetic, it might don this metallic helmet.
Skunkworks Props sculpted this helmet, which, despite its hand-forged look, is actually cast in fiberglass. That makes it just two pound, light enough to wear as part of a costume, though it likely doesn't offer much protection from Green Berets. It also has neat detail work near the muzzle in the shapes of various weapons. Now we just need to decide whom the Predators would be more likely to attack during the Victorian era.