The 757 and 767 are so similar that they even share the same type rating. This means that pilots only need to go through the certification process once and they’ll be good to go for both the 757 and 767.
One interesting story I’ve heard is that you enter the flightdeck by stepping up on the 757 and stepping down on the 767. This compensates for the difference in size of the aircraft and allows the pilots to have a similar visual perspective of the outside world on both types.