In 1961 Air France was in a "pool" agreement with TCA/Air Canada. This was a kind of early code-share. There is a chance the Paris-Montreal flight you mention on the DC-8 was in fact a Trans-Canada Airlines aircraft.
The Paris-Los Angeles flight sounds like UTA, as they had a large south-pacific operation, and the aircraft would have continued to the south pacific. I would agree with "Unique" above that the aircraft was probably a UTA DC-8.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!