Get the rest of the files here: http://www.thingiverse.com/thing:854906
For those without a dual-head printer, this is a window insert for the eye so the 'glass' can be a different color.
Print the 'eye_window_DUAL_frame.stl' from Gowanus Monster to use with this. The frame is not 100% symmetrical top-to-bottom, so try the insert in both orientations to get best fit.
NOTE: I removed the porthole insert since they added it to the main model downloads.