L4D Zombie NPCs?

Has anyone made some L4D Zombie NPCs? If not, could someone make them? I think having something other than the Headcrab zombies would be awesome.

That wouldn’t work, because they use animations made in a stronger engine version than the Orange Box

Impossible

Couldn’t someone just recreate the animations?

Well, either basically port or just use original HL2 animations. That’s easy, but will work for SNPCs only (if you don’t want headcrabs)