EDIT -- Just wrote all the stuff below but see you said "Aero" -- are you in Europe?
The '86 SPG has run-of-the-mill Turbo springs; '87 was the first year of actual "SPG springs," which are stiffer and lower. Either get a used set of those (they must have a silver, bronze or gold paint mark on them) or get some aftermarket springs. Any aftermarket springs will be at least as low/stiff as the SPG stuff. Check out the classifieds at saablink.net, saabcentral.com, or maybe saabnet.com.
Performance shock choices are limited in the U.S.: either Konis, which are expensive, or Bilstein HDs, which are cheaper but also somewhat stiff in compression, so the ride comfort isn't as good. If you get Konis, set the rears on full stiff. Another option, which I don't recommend but which is cheap, is the white KYB shocks (not silver), which are very stiff in compression; I can't wait to get rid of them on my daily driver.
The front swaybar can be made considerably stiffer by switching to polyurethane bushings at both the outer and inner attachments. Buy poly outers from anywhere Saab parts are sold (I prefer www.eeuroparts.com); buy the inners from www.sasab.com, in Oregon.
Perhaps most important up front is the alignment. The cars come with 0 or even positive camber from the factory. Get some spare shims from a junkyard car and dial in about -1 to -1.5 degrees camber, and set the toe to close to zero, slightly toed in. You'll like that mo' better. Oh, but before you start messing with that, inpsect the RH upper control arm bushings to ensure they're not failing, which they tend to do due to heat from the downpipe. Don't bother changing the lowers or the LH uppers (VERY hard with the engine in the car). Also make sure that the ball joints and tie rod ends are in good shape before an alignment. If you need to replace ball joints, DO NOT buy the cheapest ones, which are made in China and are junk.
I buy Moog/TRW stuff and have had good luck. (It looks like eEuro is selling only cheap or OE; try RockAuto for more sellection.)
The rear swaybar bushings die but are very expensive to replace from Saab. IIRC, you can get poly for them but they, too, are $$$. Inspect the upper control links at the rear axle.
The rear upper link bushings at both the front and, to the lesser extent, the rear, fail. Scantech, which makes lots of aftermarket stuff for Saab/Volvo, sells some that are crap but will last a couple years. OE will last longer but for mo' money, of course.
Meanwhile, inspect all vacuum lines underhood, and replace, as necessary. They commonly split at the nipples. Also, check your base boost -- it is usually low on a used car and, when adjusted properly, makes the engine a lot more responsive. Ignore web-based advice to buy a fancy gauge -- just adjust it so the base boost goes to the middle of the orange. If you always use premium fuel, set it a bit to the right of middle.
Put a Mity-Vac on the line from the manifold to the vac. capsule on the distributor to make sure it holds vac/pressure. If not, get another one on there. Confirm base timing is at 16*BTDC while you're at it -- the timing hole is hard to get at, so be patient.
Test the throttle switch to ensure that the WOT position works. If not, you could eventually hurt yo motuh.
I would also change the brake fluid, including the clutch circuit, if you don't know the last service. Coolant, too. Geeks use spendy Saab coolant (blue crap from Europe), but the point is to change it -- it's more important for the 2.1L motors 91-93.
I would change the gear oil every 20k miles or so, and use synthetic (I use Redline MTL). If you live where it's hot and drive, um, in a spirited manner, the MTL will thin out. If that's the case, cut it with some MT-90. Shockloading the transmission by doing drag starts will certainly hasten the demise of the gearbox.
. I'll take some photos over the weekend.
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