Your 91' has screws? Hmm..in the 92 they use 3 nuts (which are still hard to get to), and then the whole speaker unit in the rear deck comes out through the trunk... What I had to do to work in the akward position was to lay on my back inside of the trunk to work.

In terms of the speaker grills, I know that the factory fabrication with the 1992's don't allow for the aftermarket speakers to just show, because they made the hole that the speaker extrudes up through the deck too big, so I know with mine I had to leave the grill on (which I wanted to do for security reasons).