The sketch "Crash" is hovering over is the the one that became the final concept. He modified the upper palate and removed the extra teeth. As as far as I know, anyway. But.... on the other hand he could've redrawn the whole thing without the extra teeth, but they had limited time to create the Predators for "P2," so I don't think starting over would've been ideal. Unless he's like super fast.
That's a good point. They could've used Shellac. You can buy clear shellac or "Amber" Shellac (which would've accented the gold aspects of the helmet). However, Shellac is not water resistant, and scenes involving water probably would've messed with the helmets finish. I dunno.