1985 900 turbo 16, B202L, 160horses on paper (dynoed 190), bought at 301000km, sold at 686000km.
Also have had a 1989 9000 turbo, B202XL, a 9000 aero, a 900 turbo 8 (B201), 2 Saab 90, a Saab 9-5 LPT, a 900i 8V, and a few more, (including 9k v6 and 900 NG v6, but these were Opel engines).
In total roughly 750000km driven on all possible variants of Saabs H-engine.
8V, 16V, carburator, K-Jet, LH-Jet 2.2. and 2.4, Trionic 5, Trionic7, you name it. I've had them all. Even the rare B212...
Trust me, oil change interval fitting the driving conditions is much more important than which oil you use.
Any modern-ish oil with HTHS >3.5 will be fine. Use synthetic with turbos. Never beat on turbos when cold, drive gently until warm - and after demanding power, i.e.high boost and/or high rpm, let them cool down before shutting the engine off.
Don't mess with your knock sensor or the APC potentiometers. Never let the engine run lean. Make sure you run correct ignition timing. Change spark plugs from time to time.
That is all. Keeping these engines alive for ridiculous mileage is not very difficult if you care for your car just a little bit.