We have engines that over heat, but that just make's it so you can use wep. (and of course the wep is what makes it over heat)
The high G gun jams would just be annoying, games like red baron has such effects way back in the day, and unlike two vickers machine guns, it would be realy hard to unjam guns in your wings.
Also dunno how much people would like to be firing and have there guns jam, not to mention the code base would make the gun "damaged/broken" so if you did land for rearm and such, your gun would probably stay broken.
Altho, one might think while the crew is putting more ammo belts in the plane, they might be able to change out jamed or damaged guns.
Im not sure how ground crews treated such things in a front line combat situation in wwII.
Anyone know?