The top panel you are referring to is a player tracking closeout (IIRC). It covers casino only additions such as a player card reader, rewards keypad and ticket printer on some machines. Mine is covered with a black plastic panel affixed to the mounting panel.
Just from your exterior picture it is apparent that you are also missing three buttons (bet one, spin and bet max) as well as the reel #1 assembly (and reel strip) as well as the max payout sticker above the left reel. You interior picture is too close to see of you have the bill validator or cash-can but it appears the housing and DBV PS is there? You didn't include a picture of the interior of the door but I'm wondering if you might also be missing the coin comparitor?
Mose all these parts are easily available online through the NLG supporting vendors or the classified section.