Multiple sources within the Federal Aviation Administration, Boeing and Congress say the jetmaker may not get the largest 737 Max variant, the Max 10, through FAA certification in time to hit a crucial deadline that if missed would trigger a new tighter safety requirement — from which Boeing wants an exemption. Missing the year-end deadline could mean having to substantially revamp the Max 10 cockpit systems, a redesign of the aging 737 flight deck that the company previously declared impractical. While Boeing’s lobbyists have not yet officially asked for congressional action, they will likely…