I guess a couple of thoughts with this one.
In the years this craft is supposed to have existed would they have used glass?
I can see what you are getting at though in trying to find something thin enough and clear enough so you can into these areas without any distortion.
Glass would have to be very thin and the only product that comes to mind would be what they used to call "slide cover slips". Thin as thin glass squares that you covered specimens on a microscope slide.
Would you be able to cut it to size? Well that would be a test and a half.
Your other and safest option would be something like a thin clear acetate sheet to cut the window shapes from.
If you search on that you can find sheets of this as thin as 0.1mm upwards.
Tony
Happy Modelling
BUILDING: Hachette Spitfire Mk 1A, Constructo Mayflower
SUBSCRIPTION COMPLETE (Awaiting building): USS Constitution, Sovereign of the Seas, 1:200 Bismarck (Hachette)
COMPLETED: Porsche 911, E-Type Jaguar, Lam Countach