Apple PC Serial and Parallel Card - Manual (Page 33)

Preparing the slots
7 Remove the metal port access covers for the slots you need.
If you are installing the PC Serial and Parallel Card at the same time you are
installing a PC Compatibility Card, remove the metal covers to the first two
PCI slots.
If you already have a PC Compatibility Card installed in your computer, then
unscrew and remove the metal covers to the second PCI slot.
8 If you have a card in the third PCI expansion slot, remove it.
You will have more room to install your PC Serial and Parallel Card if the
third slot is empty. See the user’s manual that came with the card for
instructions on how to remove it.
Port access cover
Second PCI slot PC Compatibility Card
33 Installing the Card in a Power Macintosh 7200, 7300, 7500, or 7600