My FIL was looking at my truck the other day. He's a engineer for GM. According to him, the rear lip on the upper back of the cab of my 63 is the inspiration for the trim on the 2020 Chevy trucks.
You can see it in the last photo in this article:
http://www.trucktrend.com/news/1812-...d-high-country
and here:
https://www.trucks.com/2020/03/17/re...ado-competent/
He says the angle is about the same. While he didn't work on this truck (he worked on the SUV), the design team is the same. His brother worked on that team early on.
He's always got an interesting tidbit of knowledge to drop.