Moved this topic to the proper Forum Section.
I'm not famiiar with that particular mod pack, and I've never heard/seen anything about a mod eliminating the Strutter's rear gun (although people have experimented with altering some of the aircraft to resemble other aircraft that aren't represented in the game's stable of aircraft types). If you have any mods whose stated purpose is to add a "new" plane type/variant, you might want to check those as your initial suspects. Otherwise, your best bet is probably to deactivate all your mods and then add them back in one at a time until the problem appears (a very simple process using JSGME). Once you've identified which particular mod seems to be causing the problem, we can focus on looking at it to see what might be going wrong with it.