I haven't posted here for a while because I was on a break from the project, but I started on it again recently so here's an update.

I made 3D mockup models of the helmet and visor to fit the parts to. They're not meant to look like the real parts for say printing as I have the real helmet used for the original prop but instead it's design support. That's why I only made the frame for the visor that meets the added parts.
This is common practice in Engineering CAD design and as it does there, it helped me a lot to find where and how some parts meet.

Because of that I've changed the shape of the ear pieces some to better correspond to the originals, mainly the lower line now meets the edge of the helmet instead of sticking out a bit below it.
I also lessened the thickness of the piece and the chamfers.

With that done I added the triangular... what are they, buttons at the back curve of the earpiece? 

I made the small nubs, they kind of look like Zoid nubs, don't they? :)

Then I started making the other plate inserts and the detailing on them, but it's only halfway done so far.

The hole where the curcular cross piece goes is left out here both because it's not fully finished and also to show I'm letting it be a secondary air passage, hearing aid hole and possible secondary backup fan system placement. 

I need to be able to wear and walk around in this thing all day on Cons. The cross will have a black filter fitted behind it. More to come on this when it's finished.