NECA T-800 modification

I was browsing ebay and found a 1/6 scale endoskeleton by NECA (National Entertainment Collectibles Association). It is a collectible item, but it looks and feels like a toy. I mean, It looks pretty good, but it could become even better with some modifications. I want to get rid of the toy look and improve details.

I searched youtube, and found this.

This guy was doing what I wanted to do. So I tried to make similar modifications myself with the materials I had at my disposal.

Improvements I want to make

Remove head screw for battery compartment
Fill screw holes with putty
Replace head joint to increase movement
Open the chest
Widen shoulders
Improve hip joints to increase movement and posability
Remove material from upper arms
Scratch build new forearms
Scratch build new hands (original are too bulky)
Improve upper legs, add details
Scratch build new feet
Replace eye LEDs
Scratch build jaw pistons
Add hydraulic cables to pistons to add realism

So the first step is to take it apart.