No the upper mount bolt holes are spaced differently.

 

Are there any other differences between the strut housings, coils, and hubs? Can I use the 900 mount with the 9-3 housing/springs? How about rotors and brake caliper mounts - are they the same?

 

99-3 springs are different in the front. Conversions are possible. See this: http://photo.platonoff.com/Auto/20070511.Saab_NG900_Eibach_Springs_From_a_9-3/

The brakes will fit and might possible be a slight upgrade if its the '96 you are working on (which also might need a tweak to the rotors to fit). There was a change in '96/7 ... Jake can probably tell you more.

 

The units appear to be the same, they use the same bearing and hub, could be something as stupid as the abs pickup mounting hole. Where you have both there do a quick measure. the springs will be an upgrade, struts appear to be the same. the difference between them could be so slight.

 

False, like Bob mentioned the springs are tapered different between the two, so the lower spring perch on the housings are different. Along with the upper spring seats (the ng900 has separate bellows and rubber spring seat, the og9-3 has a one piece design).
The strut inserts are different between the two to fit in the different mounts that are mounted to the inner fenders in different positions.

The bearings are the same, so if that is the problem you could swap them, but since they are available new for $10 it doesn't make sense to pull them all apart and put used ones in (you could probably just regrease the ones on the ng900 anyway).

If the mounts or the inserts are bad then you will have to buy new ones the ones from the og9-3 wont fit and can't be made to fit.

Like Bob says the springs can be made to just about fit, but unless they are broken on the ng900 or performance springs on the og9-3 there is no point in doing that (keep in mind they might be of different spring rates too).

1996 and earlier 900's had smaller brakes (284mm vs 288mm) so not really much of an upgrade, the calipers are different for the different rotors.
Some of the early 900's had much bigger hubs and the later 288mm rotors wont fit over them.

 

I know I'm digging up an old thread, but has anyone measured the differences between the stud spacing on the NG900 and 9-3 strut mounts? Are the positions of all three studs different between the two, or could a hole or two be widened to accommodate a 9-3 mount in a NG900? I only ask because I have set of stock Viggen springs that I want to put in my NG900. If it's definitely not possible, I'll source some rubber rings like Platonoff used on the upper mount, and try to find a pair of the now-discontinued 9-3 upper spring seats/boots.

 

Jeremy:

The two short side studs are the same distance apart. There's a larger difference in stud location on the long side of the tirangle, about 3/8". You'd have to elongate all the holes to center the strut, maintain camber, and avoid moving the long side stud into the curved part of the strut tower. So the inner hole needs to move 3/16" closer to the engine and the outer holes move about 3/16" towards the fender. You will also need to mod the strut-bar holes.

If you end up out of the reinforced area of the tower, you'd need to weld some thick washers on top. Otherwise it looks very doable to me.