jayemm
This sounds to me that there has been a mis-understanding between your selfs and the engineers.
I can only think of two types of AI that are likely to be fitted to your aircraft and both types are avalable, new or OHC.
It is very unlikely that someone would have fitted an AI that was not one of the two "standard types" so I would advise that you talk to your engineers face to face and get this sorted out, if you have any more questions take a photo of the AI and the hole in the panel, email them to me (with a rule in the photo for scale) and I will try to offer some more advice.