You're right.... The footage was all (supposedly) shot from the Lexington. This makes me wonder if it was not shot from Hobart instead, because the shot of the motor launch approaching the filming vessel is clearly one which shows two "large" caliber guns trained outward.
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The USS Lexington had her 8 inch guns replaced by the quad 1.1 inch light AA guns before the Battle of the Coral Sea. The only ship on the Allied side with twin 8 inch turrets was the HMAS Australia. HMAS Hobart was also present and would have had twin 6 inch turrets.