First off - I picked up a 93 aero recently and, as I like to comment every so often - 'they are real and they are spectacular'.. :) ..
Secondly - you may have got boned at the shop. It may be time to develop a new relationship elsewhere or see if the wrench-meister in question is open to your picking up a manual for him and sending him some good links as repairs come up.
Basically - the head gasket and turbo failure are most likely related in that almost all head gasket failures are related to over heating. If you do not see a new thermostat and three-way thermo-switch on your bill - your shop doesn't handle this sort of work often enough.
Once the engine was overheated (which is usually a couple of times in a row before the end comes) - the turbo bearing and seal are starved for cooling fluid in the right range and deform. The next time the engine lights up - zap - whatever was holding the liquids out of your turbo is released and - it's so long hoopy overtaking maneuverers and hello police officer - yes I'm waiting for parts but needed to move the car - thank you for the warning - I should be able to get it fixed next week and I'll park the car until then.. :) ..
The sad part is that the shop may well have been able to rebuild the turbo with fresh seals and bearing at the time - but I fear is may be too late as running like that for a short time will damage the impeller and housing so that it is cheaper to get a fresh turbo.
Normally - (well since the mid 80's at least) the SAAB turbo bearing is water and oil jacketed and requires no 'one minute' cool down period at shutdown - which is not to say that it might not be good for it - but it is not required. It would concern me greatly if my wrench-meister didn't know that.
Where you appear to have got shafted is that the shop should have known to pull the turbo and inspected it at the time as it may have saved you considerable labor and costs to simply replace the whole power unit with one from a wrecked model of similar vintage.
As it is, you have simply paid for a single heat related gasket failure and will now pay again for the same heat related failure - with likely a few more to come.
127,000 miles is not new - but assuming the body is good - I would have pulled the block and done *all* the gaskets, seals, pumps and timing chain gear at once (which is considerably cheaper than working on things as they fail). I also would have costed that job against a known good engine and turbo out of a wreck and picked the one that looked best choice at the time. Cheaper to pick up a known good power unit - vs - I know everything vital is done in my original engine.I will be pulling mine from the aero and doing much the same thing when it needs something heavy like a a clutch, additionally dynamically balancing the crank and pistons so I can then pull the balance shafts. Longevity is important to me and work like that in an aero can be recouped if you have to sell it.
Sorry brother FU - the silver lining here is that once you do that more encompassing job at a shop that knows the machine, you can be fairly comfortable that the body will rust away long before the motive unit needs serious attention again.