Question about body style change

[Bigb401]

Hey guys I got a 72 blazer and am familiar about those years. I recently seen a 65 2wd pickup for sale and been thinking about adding it to the collection. I was doin a little research and checking out others pictures and noticed that doors and windshield glass looked different. It looked like on some that the windshield glass curved back toward the doors more. Is this a common customization or did the earlier years have that different style from the factory? Also curious to know what other changes gm made during this generation of truck. Any Info from you guys would be great.....thanks.
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