I guess folks here are "old", eh?
The route these guys used is the road. Don't know of any trails that go all the way through the ~135miles. The Denali Hwy isn't maintained in the winter but some of the lodges, etc. along the way groom portions. Then snowmachiners, trappers, skiers, etc. do make pretty good hardpack for a bike if it has fat tires. Since the snow is very dry, takes about 10+ inches to make one water inch, once packed it makes a great road.
Over the years I've spent a fair amount of time outdoors summer and winter. Yep, when it is -40 F/C it can be challenging, but doable and even fun. But I've never used a bicycle as my transportation. I was hoping someone here who was past the immortal years had and could pass on some tips.
May never do it. But the idea is intriguing.