According to my sources, the rear window was removed on all but a few of the early F6F-5s.
Are you talking about the hump that is just below the cowl flaps on the -3? That was removed on the -5, although I am not sure why that is. I will speculate that the reason for that is there was a change to the exhaust manifold.
Amazing that you are in Waterford. I remember the town a little, but I haven't been back there in probably 15 years or so.