I currently just bought a 91 Trans am Convertable off my firend recently and i was wondering if there was a cover that starts from the back of your front seats to the back of the passanger seats seat when the top is down ive seen them on other cars but never on a firebird i know wild copper has one but is down for reconstruction here is a picture if i was confusing:lala:

 

The top that you've got there looks like the tonneau cover a 3rd party vendor made when they converted early thirdgens into convertibles. It had to do with the way the top mechanism worked. I believe that that piece runs all the way to the back of the trunk (it replaces the trunK). I have never seen what you're talking about made for a thirdgen in your year that only covers from the tonneau forward. I also don't think i've ever seen one that just replaces the tonneau on your model, cause i own a 92 vert and remember looking around for something similar. when all is said and done though, i don't think it would be all that tough to fabricate one out of glass (or pay someone to do it for you) using the existing tanneau cover

 

Is your car an ASC conversion? If so, I am willing to bet that the trunk you you pictured will not work without some significant modifications. I could be wrong...

Your ASC sticker should be on the door jamb off the drivers door:

 

That is from wild copper they replicate Knight rider cars and i guess it went drop top one day and that covered the back so he made it i was just using the picture as a example incase my disricption was confusing