If you're not talking about non-stop flights, but flight number,
ROYAL BRUNEI used to operate FRA-DXB-BKK-BWN and
I think LHR-DXB-BKK-BWN with 757s, in the early 90s.
The flights still exist, but now with 763s.
Not strictly 757/767-related, I remember to have seen
Wardair Canada 727 C-FFUN in DUS several times on flights from Canada (not bad, eh ?!) , and if I'm not mistaken, Sterling
used to fly fly Caravelles all over the world. Maybe our
Danish / Swedish readers can contribute more details...