Replacing brake lines

Ok kinda a newbie to the A body world but my son's 60 Dart needs all the brake lines upgraded to stainless steel now I recall seeing an episode of Graveyard carz and the tech was installing brake lines on maybe a B body and he was doing it before the engine was installed. I REALLY don't want to remove the engine so how difficult of a job is it to install the new lines with the motor still in the car?