With the on going grounding of 737 Max, if some airlines want to change their 737 Max to 737 NG what modification is needed? The main change would be the engine and control system. Any other change is needed in order for the plane to be re-certified for flight?
This page lists all the functional differences between the MAX series and the previous 737 variants. There are quite a bit of substantial changes like the reshaped tail cone and electronic bleed system. Not only are the engines different but the mounting pylon was changed to account for the new engines so you likely cant just "bolt on" the old engines. Even the cockpit has a different panel.