Isnt 757 and 767 cockpits very similiar - easier for pilot training?
Indeed, the two share a type rating "Boeing 757 / 767", however that does not mean a 757 pilot can fly a 767 and vice versa, there is a short differences course.
But in general they are regarded as the same type from the flightdeck perspective once the course is done, and you can hold on to a 767 rating (once differences course is complete) just by doing alternate sim checks every six months (e.g. 757 in January, 767 in June). In other words, without actually flying a real 767 on a regular basis.
The differences, from a pilot perspective,
can be found here.