This is really amazing looking. It has some differences to a direct cast off an original, but it definitely has the "look". And that's one of the most important things. I'm really amazed you were able to capture the likeness of Vader. - I know likeness is kinda the wrong word to use here, but it kinda fits, so I'll go with it.

Gonna be great to see this paired with the dome.

I know it may not be exact, but I was given some mesh from this source and it worked fine. It's about the correct size and shape. If you can't find the original type, you can always try and see if you can find this:

, on Flickr

Cool to see the two together. Yeah, I have seen many tackle face and dome separately only to realize they didn't fit together long after the sculpting process was over and they had already made molds. If I could save someone from experiencing that again, all the better.

I can see where the most work needs to be done. The crown itself seems okay for now, but where the crown meets the bottom skirts of the dome, you need to make the shape curve inwards a bit again, before the separation groove, and then curve slightly outwards again. You should probably also slim down the skirt sides, as the inside surface seems to be pretty close to where it should be, so the outer surface shouldn't be too much further out than that. Go slow and try to stop completely when you reach the halfway point between the current inner and outer surface and see how that looks.

This is literally the best original Vader sculpt I have seen to date. Well done sir, well done.