Man... I remember the very first set of Bionicle Toas. I feel old. Anyways, nice modification! I always hated the underwater Hewkii set becuase Lego did a poor job of armoring him. What you've done here is fix that. Great job! The only suggestion I have is if you added chains to him. The chains are one of the few things I actually liked about him. Overall, 5/5!
I never bought Hewkii Mahri; I would've used his head if I had. I kinda wanted to mix Hewkii Inika and Mahri together...or something. I think in the end it just looked kinda like Hewkii, so that's what I titled it.