I looked at my pile of 3Com Etherlink cards, and found these two notes:
- 3C-PC-COMBO-CBL (RJ45 + Coax dongle) -> works on 589D/E.
- Foxconn 07-0408-000 0035 (RJ45 dongle, number on cable) -> works on 574BT.
I think I've tested these around and it shouldn't hurt trying, but it probably will only work with the original dongle.
(These dongles and cryptic model numbers (between visibly almost identical cards) are a true pain, especially if the locking clips break or there is a bad contact)