It looks to me that it has a sort of swiveling dish-like structure inside the 'mouth' that lights up when it fires. However, there are scenes and photos that show no 'dish' and only a sort of hole where the dish structure would presumably plug in.
I think it might be an optional part, or something that was originally there, but was lost or broken over time. IIRC, the wing up/down mechanism also stopped working eventually.
Comparing the pic Eric posted with my pics, it seems like that may be an entirely different gizmo than the 'other' one. I don't seem to see any areas where the orange 'rectangles' texture might show, or be illuminated. It also seems too 'domed' to me. If I had to guess, I'd say that was a prototype or replacement part.
Seems to me that it depends which version of the studio model you want to replicate?Sometime between STIII,the TV shows and films it appeared in that new parts/details were added into the KBOP and the main canon because the photos are showing different details.I often wondered if ILM built a much larger secotion of that part of the model for close ups?I've not seen or heard anything about if they did that or not?