767 was the first two engine certified for ETOPS. ETOPS specifies how far, in flight time, an aircraft can be from a suitable landing strip. There are many factors that determine how long that can be. Usually it is 180 minutes (for 2 engines, I believe more than 2 engines can go up to 240 mins) but several factors can lower that to 120 minutes or less. Each airplane is given special maintenance inspections prior to each ETOPS flight. A reduction in ETOPS time can be caused by unreliable aircraft at the given airline. Let’s say airline X has had a lot of maintenance issues this can lower that airlines ETOPS time. The other interesting thing is the “suitable” landing strip. While the airport can have the airplane safely land often times it can be at an airfield where there are no passenger services. A few years back a Delta 767 landed at Cold Bay AK. I think the population of the town literally doubled when the airplane landed. Talking to the pilots it was an interesting event! The town opened up places for the people to stay, like the fire station etc. Delta dispatched another jet to pick up the passengers fairly quickly but Cold Bay is a long way from pretty much every where and if I remember correctly the pax were there for about 12 hours. As far as limiting altitude when flying over the North Pole I’ve never heard of this. I’ve been to about N80 and never had to fly at a lower altitude.