Daniel.
I'm in possession of a magazine;
"Profile Publications"
The Armstrong Whitworth Whitley, Number 153
Retail Price, wait for it, 2 shillings
Publishers:
Profile Publications Ltd,
PO Box 26.
1A North Street.
Leatherhead
Surrey.
Regarding your question of the turrets?
On page 6 of the above mentioned magazine, and I quote.
"A few of the 40 Mk. IVs/IVAs built retained the old A.W. manually-operated rear turret and were known as Type 206s, an example being K9054, a machine eventually scrapped at Cambridge in 1943".
Mk. 1.
I believe the Mk. 1 had the manually operated nose and tail turrets each mounting a single 0.303 in Vickers machine gun.
Mk. 2
No idea
Mk. 3
This Mark had the manually-operated A.W. nose turret with the single Vickers gun replaced by a similarly armed Nash and Thompson power-operated turret. The rear turret still retained the A.W manually-operated turret.
Mk. IV
This Mark, commencing with K9016,had a Nash and Thompson power-operated rear turret mounting four 0.303 in Browning machine guns
Hope this information is of some use.
Alex.