Sounds like you're on the right track, the 'ol dead six approach is aptly named because that's usually what the result is. High side attacks aren't a bad way to go, I also like to climb above the bomber, get a little in front of them and roll over in a split-S and come down right on top of them, passing over the top turret as I'm firing.
This makes it hard for the top gunner to track you since the gun only elevates up to about 90 degrees, as you pass from in front of the gunner position to behind it he has to rotate 180 degrees and it's a hard shot. From the attack POV you can get a shot at the cockpit or engine/wing root and if you're aircraft has a decent gun package score some damage on the bomber or bring it down.
Attacking bombers can be an exercise in patience, but one where patience is generally rewarded.