does the 900 siu2 sid unit fit in a 98- saab 9-3

No, the consoles are not identical.

Edit:
To clarify, the issue is primarily in the compatibility of the units. Each piece of a Saab is mated for THAT Saab and no other. It is what makes stealing parts from one so fruitless. l am not sure how one would go about mating foreign parts with another car but that may be difficult, seeing as the whole idea is to prevent this in the event of burglary.

Yes it does. Need to replace the bracket. But it does not have the correct info.

l have the place you can get your sid fixed.look at link below. l have used him for long time.So far no problem.