Note the lower of the above two photos that Jarink has kindly provided and compare it with your profile. I'm really wondering where you came up with that detail info on the nose weapons.
the gun bay cover was held in place by Tzus fasteners, no hinges as far as I know. The cover was a higher tensile aluminum and tended to have develop a lighter shade (and was thicker) than the rest of the forward airframe skin. This lighter shade particularly developed in the tropics.
The offending 'hinge' is long gone. I was misinterpreting a heavily pixilated picture. The .50 Cals now have covers as fitted to the later variants.
I've now sorted out the wing; all line drawings being incorrect giving it too much chord thickness and too much dihedral. Just need to work out the gun sight details next...