Interesting, I wonder if a Kiowa, or for that matter, Cayuse, Wasp or Gazelle could be fitted with 20mm in such a way. It would look cool on an Army or Navy Lynx, or Seahawk, the Blackhawk or for that matter the Chinook, Stallion, or Super Stallion would look great with a pair of them.
What would be good, but maybe difficult to model, would be a mount that permits the gunner reasonable arcs of fire but also permits the gun to be locked in the forward position for the pilot to aim and fire.