you have to look in the "out" file ,if there is one available" and hope that the mesh your looking for is labled as something you recognize like "topwing_L or something. Otherwise you will have to use trial and error.have a look at the Nieuport 17 with the wing mounter lewis,it has entries added in the gun section that edit out the deck mounted vickers mg and it has the wing mounted lewis added as a "pilot". as for adding an extra lewis to the brisfit visualy or fixing the radial engine on the Foker D.III that would require the original modler or someone with access to his original max files to redo the model. once exported to lod format it's essentialy imposible to redo the models.