The Kanohi Isima is the mask of Possibilities in which the noble version allows a lesser percentage of the desired event to happen compared to what a Great version could have pulled off.
Here are yet more noble masks to equip to the Exatoran! Info I've used is taken from BioSector01 and discussions among friends in the Bionicle community. Feel free to point out mistakes in my understanding of the lore.
I did the prototyping this time for this mask straight out of shapeways and it fits the Metru head well. It slightly collides with the Mata head, but with a little force and if you are willing for the mask to bend a tiny bit, it fits.
DISCLAIMER: due to the new sanding process of Shapeways, the Versatile Plastic may come out too thin or too thick. This result is completely out of my control and I chose to stick to these measurements for if by the rare chance that you get the thin axles, a good 3 coats of hobby acrylic paint can fix it. Better this than a very large axle that breaks your Bionicle and Technic pieces. I myself received thinly printed axles on my personal order, and came up with this solution myself. Please recommend better solutions to this if you have found out any.
Bionicle is still a trademark of Lego and I own nothing but the design concepts and 3D models I make to add to its lore.