Well, with the ANH stunt/hero difference, the ESB and ROTJ versions and the way each individual movie helmet was assembled in slightly different ways (higher/lower brows, differently cut out holes for eyes and frowns, different ear trimming), it's not really possible to say which version would be the stormtrooper helmet. Stormtroopers aren't as standardized as people tend to see them.
Which version are you trying to replicate? That would be a more realistic approach, methinks.