The existing 757 and 767 pilots will be able to fly the 767-400ER as a common type, I would assume the 767-400ER has a "gauges under glass" concept in the cockpit like SWA's 737-700s, where the 777ish displays are programed to read more like the older style instrument panels in the existing 757/767s.
Common Features Offer Competitive Advantage
The 767-400ER brings all the competitive advantages of airplane family commonality to an operator's fleet. This derivative shares common features with the rest of the 757/767 family of airplanes, including a common pilot type rating between all 757s and 767s. This allows any pilot trained to fly one model to be qualified to fly the other model with minimal additional instruction. Compatibility with the 757/767 family means that operators can gain better access to the demanding, medium-size market (200 to 300 seats) by matching the appropriate airplane to variable requirements. They can also improve operating efficiency through lower training requirements, greater flexibility in assigning flight crews and reduced spares inventories.