Hi Jack,
Have to disagree with your comments about the RNZAF Sunderland Mk V/MR5, being extensively modified internally.
Certainly the W/O suite was modified, and a couple of additional instruments were added to the Instrument panel. The rest of the Airframe was stock Mk V. The Balsa Upper sub bulkhead was still there.
The dual ADF Loops were to aid navigation over the vast Pacific.
The W/O position was still occupied with a signaler.
The Upper Turrets were removed from production circa 1944, as the threat from the Luftwaffe decreased. I have photos of both 270 and 490 Squadron Sunderland’s in West Africa without the upper turret.
Not all Sunderland’s such as Mk III’s had fixed bow guns either.
Only those that operated from bases in Britain had them, whereas those flown in places like West Africa did not