I am researching 11 Sqn's 9 April 1942 attack on the Japanese carrier task force off Ceylon and I'm wondering if all of the squadron's Blenheim IVs had the newer dorsal turret with two Browning machine guns. The serial numbers of the aircraft were:

V5992, V6010
Z5868, Z7506, Z7640, Z7759, Z7771, Z7767, Z7640, Z7803, Z9574

Any help would be greatly appreciated.