Actually there was another thread by someone up there who was having an odd idling problem where the car sped up when cold, he was also in this -50*C area and he said after leaving the car plugged in and glowing the GPs 6 times (I suspect he didn't wait for the relay to shut off) it started with 2 cranks.
He has a 79 300D which is a nonturbo. I'd think that synthetic oil is a must when it is that cold.