Here is a link to a photo of supposedly an 84 tank, showing screens inside.

http://images.thesamba.com/vw/gallery/pix/889180.jpg

Here is a link to a photo of a 90 tank opened showing screens.

http://images.thesamba.com/vw/gallery/pix/446713.jpg

Subtle differences between these but both show a screen on the inlet and
another on the return tube.

There were 2 different fuel tanks during 84 since some that year had the
small filler pipe hole for the newer plastic filler and some the older
large hole for metal filler pipe.

Since Bob had an 84 tank photo without screens perhaps this answers one
of the mysteries of the square fuel filter!

Mark