I used DryDex Spackle to fill all the layer lines and give the head a textured effect.

I then primed, painted and used some graphite powder to give it a weathered look and sealed it with some clear coat.

Assemble the head as shown and secure the pieces using M3/M4 bolts with brass heat inserts (or if the holes are small enough, you can manually thread/tap them)

Press fit the 8mm Shaft Collars in the Jaw and slide the rod in. (You may have to make a small notch to access the shaft collars set screw and secure it to the rod). Once everything is tightened down (including the gear) ensure when you manually turn the shaft gear it moves the jaw.

Set your MG996R servo to 0/180 degrees, depending on orientation (the servo should spin clockwise if you're going to set your jaw to fully closed as a default position). Add the Jaw Drive Gear to the servo, then fully close the jaw & add the servo to the slot in the Head Base. Test your servo to ensure it moves the jaw correctly. (I had some slippage in my gears, but I used a zip tie to act as a tensioner).