I think the 540 model is a Pentium PCI based one, so it would not run on a Nubus 486.
If you can take a picture of the card I might be able to help identify it. My 486-100 card has one PCMCIA slot on the end. I also have a full length 486-133 model which was the last Nubus one made I think (Model 340).
If you can take a picture of the card I might be able to help identify it. My 486-100 card has one PCMCIA slot on the end. I also have a full length 486-133 model which was the last Nubus one made I think (Model 340).