Okay. That's what I was afraid of. (When I bought the wireless card its description was somewhat vague other than it came from an Intel iMac.) Eh. It's at least cleaner having it internally rather than having to use the USB dongle.

BTW, on the remote chance that anyone finds themselves in a similar situation, I found screws suitable for holding the card in place (the posts were empty in my Mac Pro) inside an old laptop CD-ROM drive, around the eject solenoid. Scavenger hunt!