Your best bet would be to open the case and:
Determine if you have a slot open "below" the PCI slot such that you know if you HAVE to use a single slot card, or have room for a dual slot.
Determine if you have the width for a normal card or a half height card.
Use a measuring tool of your preference to determine the open space from the I/O to any interfering cables, case, etc. and use those measurements against the provided ones from the manufacturers cards you are considering.