Thank you very much.
One small point, though. I don't think the G-1 had the chin .50 cals, only the four 20mm.
http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2981
That source says that it doesn't have it^^ however I have multiple sources saying that it does:
"The A-20G, delivered from February 1943, would be the most produced of all the series - 2850 were built. The glazed nose was replaced by a solid nose containing four 20 mm (.79 in) Hispano cannons and two .50 in M2 Browning machine guns, making the aircraft slightly longer than previous versions. After the first batch of 250, the unreliable cannon were replaced by more machine guns." - Wikipedia - refers to G1 when it talks about the first batch of 250.

Here is a source which supports the A-20C like turret and also armament:
"A total of 2,850 A-20Gs were produced, in three major versions. The first 250 were built with four 20mm cannon and two .30in machine guns in the solid nose and the original manual dorsal guns. The cannon proved unreliable, and so the next 500 aircraft were armed with six .50in machine guns in the nose, but still carried the manual dorsal guns. Finally, starting with block A-20G-20, a Martin 250CE turret was installed. This was armed with two .50in machine guns, and had a 360 degree radius of fire" -
http://www.historyofwar.org/articles/weapons_douglas_A-20G_havoc.html