BOAC:
Hopefully the answer to why they held at ZEDAG below 4300' will come from the CVR.
The flip-side to that is why were they issued a clearance to fly as low as 2,000 when they were entering an area where the minimum off-route altitude (known as minimum instrument altitude "MIA" in FAA Air Route Traffic Control "ARTCC" domestic ATC parlance). In that part of Alaska flights typically communicate directly with the ARTCC and on the route they were flying are typically radar identified.
The FAA and NTSB already have the answer to the question, "Why were they cleared at or above 2,000, and how high did the 'above 2,000' go?"