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Because of the shape, I think you're gonna need more than just some measurements. I don't know if you can get a good enough idea just from the frame, allowing for the gasket, or not. I thought I saw where somebody here had some templates from windows they had made. Maybe they'll come along and help. Or if somebody has the windshield out, maybe they can trace its outline on a piece of paper or posterboard and mail it to you.
I gave them my glass from the '47, and they made patterns. The new glass fit perfectly. Since '40-47 are same, you should be good. Fair, reasonable and good guy. He'll take care of you. Tell him it's the glass for the Computer Literates guy to jog his memory.