I asked my good friend David Morris if he had any photos of 6765. David is a great resource for passenger train information. He found that 6765 was never on the Atlantic but did lead the Scotian at least once, as well as train 18.
Here is 6765 at the head of train 12, the Scotian, at Sackville NB on May 12, 1977. Note the CN logo on the nose, an indication that this was the transition era where VIA was a unit of CN, before CP transferred its passenger equipment to VIA. Also note the CN RS18 as the third unit.

The complete consist was VIA 6765, VIA 6625, CN 3119, 9640, 5419, 5444, 5505, 5722, SOIREE, 1366, and GREENRIDGE.
David also found a photo of 6765 leading train 18 in "Cape" (wherever that is) on April 27, 1980. Here the VIA logo has replaced the CN logo on the nose. This is a shorter train, but notice the dome car.

The consist was VIA 6765, 15410, 9616, 5440, 515, and 5489.
VIA 6765 was retired between 1987 and 1989. As it happens, she survives today at the Canadian Railway Museum in Delson, Quebec. Here is a photo I took of it in 2005 in its original CN livery.