Front Guns in Vengeances.
Chugalug,
I fancy the whole initial production was rushed, with no proper Service trials. When the fault became apparent, it was obvious that the aircraft was far too sluggish to be any good as a gun platform, anyway, so the guns were regarded as little more than ornaments. We had a good dive bomber, and had to be content with that. For that matter, I don't think that the Stuka did all that much with its rifle-calibre front guns. (I think there was a Mark with "tank-buster" pods (40mm?) on each wing), but I can't see it hoisting those aloft and its 750k bomb.
You are right, the AN and AP series were purchased by the UK, only the EZ onwards and of course the FB and FD (Mk.IIIs) were Lend - Lease (info from Peter C. Smith "Vengeance"). I think our purchase contracts were with Vultee and Northrop direct. Frankly, I never felt the need of a front gun (but a .50 in the back would have been nice - and 2 x .50 even nicer !)
Really, the (originally) weak rear gun mounts were more of a problem, but we seem to have got those really fixed. The guns did not break away when I reduced my aircraft to scrap (story a bit further on).
Danny.