Everything is super easy.
The eye is basically an MV type lens commonly used my model railroad builders to simulate non-working lights. Its a plastic lens, that is shaped in a dome - very realistic when backed by the chrome or metal paint/part. The metal eye socket is perfectly shaped for this particular size lens - they sell two different standard mecha sizes. Once assembled together the entire eye assembly simply superglued instead of the kit part - no problems.
As for the metal spikes there are MANY options and styles of these, short, medium, long, detachable base or molded base. Lookat G-Option, Model Up or Mechaskunk parts for examples -simply drilled an appropriate sized hole and insert the spike.
I will updated this tomorrow and show you the spikes close up