Steve is right in that most any grade of Mobil-1 will work in cold weather. I even ran 15W-50 during part of one winter. Having said that, however, when things get below zero degrees, battery capacity drops off markedly, fluids thicken and engine cranking speeds are reduced. To give you that "extra" measure of security (who wants to be stuck with a car that won't start when the temperature is below zero?), I'd go with either the 0W or 5W Mobil-1; it does make a difference during those super-cold arctic days and nights which we get a dozen times or so in a typical winter.
The 0W-30 is probably overkill and works best with newer cars. I use this in my wife's high-revving 4 cylinder car and there is absolutely no oil consumption. For older cars like your '86, I'd go with the 5W-30 and you'll be just fine. Then switch to the 15W-50 in the summer. If you told a local MB dealership that you were going to use 5W-30 Mobil-1 in your car in this winter that would say "great choice".
Now that it's snowing outside, let's get back to the winter tire issue. Steve is right again -- those are two excellent choices. I've used both. In fact Luke is sending me another set of Artic-Alpins to replace the worn set on my wife's car. For your car I'd get the Blizzak WS-50s. What I did was mount the winter tires on the existing wheels (they'll be on the car 5 months here) and then purchased separate wheels and summer tires in a plus one sizing. You've got a rear wheel drive car with no electronic traction control. But if you don't want to spend a lot of money for a 1986 car, I understand that too. Good luck!