Personally I think the Lib should have been a gunship and not a bomber...
Move the pilot to the bombardier spot and keep the 35mm where it is. Put a 25mm ball turret in the front with as much range of motion up as down. Keep the rear ball turret as is (has to have a weakness somewhere). Add another gunner between the pilot and the nose gunner, who has control of Phoenix style guided missiles with Decimator damage and 100m more range...
Keep it with the Lib's armor and speed and you got yerself a bonafide gunship...
Call it the Devastator...