Was following a set of lancs and noticed something only because I was trying a low attack, film rolling, bobbing up and down. I thought it was easier than it should have been, but turns out pilot was wounded (that might explain it!).
The nose turret was firing backwards, upwards, rearwards, through the plane, slaved to the other guns.
It had no "stops" or, at least, they were very liberal ones. It shot backwards greater than 45-degress downwards, and on another attacker upwards at 45-degrees as well.
I think I might have seen some errant tracers from the nose before but this is the first time I've definitively got it on film.
http://www.nakatomitower.com/lanc_buggy_guns.zip0.96MB zipped. Unedited (didn't know if that would screw with anything if I clipped or cropped it).
I did a quick and dirty (read: low res) capture via fraps from the film viewer to show it better: