2.7 swap to newer 3.5

My son blew the 2.7 in his 2007 Charger SE, and I bought a badly wrecked but running 2009 Charger SXT with a 3.5 for a donor car to get the whole drivetrain to the rear end and computer/harness. When I ask questions locally, the dealership mechanics say the sawp won't work because the 09 has...