I think it's cool that people seventy years on can learn something from the studio that gave us Henry Chickenhawk and Yosemite Sam.
Speaking of aerial gunnery, did you know a few Mk. I Lancasters were fitted with ventral turrets? Here's R5727, the "pattern Lanc" flown to Canada preparatory to the building of the FM series Lancaster Mk. X birds in Malton.
The Lanc's #1 blind spot was underneath, a fact the Nachtgeschwader folks knew very well. Their Schragemusik install took full advantage of it. The obvious fix was the installation of something to ward off attacks from below, and nothing says "not today, Fritz" like machine gun fire.
Fired by periscope from inside the fuselage, the FN-64 install was neither widespread, nor popular, nor terribly effective. Gunners couldn't see enough to be useful, it weighed more than the aircraft liked, and added complexity.
(Looks like version 0.1 of playing with your phone while "dropping a load"...)
It appears there is exactly one of these things left. It's in the hands of a welding and manufacturing concern in the UK.
That should polish out.
One more idea that should have worked but didn't. The space was far more effectively used by the H2S blister.