By Valerie Insinna WASHINGTON (Reuters) -Boeing has signaled to suppliers that plans to ramp up production of its bestselling 737 narrowbody jetliner will move about two months more slowly than originally anticipated, according to two people with knowledge of the matter. The U.S. planemaker now expects it will produce 42 of its 737s per month starting in February 2024, according to a new master schedule that Boeing briefed to its suppliers over the past week, the sources said. Both Boeing and its European rival Airbus have laid out ambitious plans to increase production, particularly for popul…