Re westbound Lhr - Lax.
If I remember the 707-336 used to tech stop Wiinnepeg - it was always tech stopped as I recall and I think the crew changed.
It never tech stopped eastbound.
I was on the ANZ DC10, as a copilot, and we never, to my knowledge, tech stopped - the aircraft had sufficient range and en-route reflight planning was used to reduce reserve requirements if neccessary.
Sometimes payload would be restricted if there was a weight problem.
We often had a bowser standing by for a last minute top up if there were no shows.
As the sector was quite long there was an arrangement whereby the flight crew were given Lhr hotel accomodation for the two nights before the flight.
This allowed for an arrangement whereby "tomorrow's crew" could cover the standby requirement if there was a delay or the aircraft returned.
Westbound flights were generally further north than eastbound flights as the prevailing wind is usually westerly and the further north you go the wind tends to get weaker against you.
The furthest north I can remember going was overhead Clyde River on the east coast of Canada but flights may have gone to higher latitudes - we often routed north of Iceland.
In the winter eastbound there could sometimes be a problem with the fuel tank temperature and the flight engineer would move it around the tanks, to make it do work, to warm it up.
Failing that a descent of 4000ft would be required to a lower (warmer)altitude.
This was not a problem westbound as the fuel in tanks at the higher latitudes was considerably greater (and therefore took longer to cool) than eastbound.
I think from Lax we also got special high density fuel (not available at Lhr?) which had a higher freeze point.
I think the ANZ tie up came about because the 747-136 (P&W engines) did not have the range.
When the 747-236 (RR engines) came along that could go direct and the DC10 was only swapped twice per week.
The ANZ DC10 was then used to do a mix of Lhr - Bos - Phl, Lhr - Ymx, Lhr-Mia on the intervening days.
There were about 17 crews on the DC10 so it was quite a friendly existence.
As a late 20year old, the 3months posting to Auckland, for the conversion, was one of the major highlights of my career - New Zealand men wanted to go do their own things at the weekend and left behind lots of lovely young ladies!!