If Vader's suit and helmet still remains in the edit his helmet should be like this:

It is from the EFX prop collectibles company based on one of McQuarries concept sketches of Vader. Most of the other concepts for Vader ranged from a face mask (and a full head of hair) to a Stormtrooper helmet and other helmets more like the Vader we all know and love but meaner. But I like this one because it isn't too outrageously evil. less refined you know

And a very relevant link

http://secrethistoryofstarwars.com/visualdevelopmentofdarthvader.html