Hi Arty,
i'm not an expert on the Berlinetta but it looks like the dashboard scuttle to me, but difficult to say without any indication of its size?
You could have a look around these websites to see if you can spot it...
http://www.stonefisk.com/Berlinetta/buildgallery.php
http://marlin-berlinetta.co.uk/myberlinetta.aspx
If you just Google 'Marlin Berlinetta' and look at 'Images' you'll get loads of pictures to help with your build.
Good luck.......
...peter