So, my theory here is that there are two designs approved by GM that will work for the intended applications, just one of them not be somewhat true to the factory issued design.
Here are a couple of listings that show the "wrong" style master for a 1972 C10:
https://www.ebay.com/itm/12570248397...Bk9SR8TL94aRYw
https://www.ebay.com/itm/16582312265...Bk9SR8bL94aRYw
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1970 K/5 Blazer CST 4WD, Bronze, 93k ACT. miles, 350, 4 speed, positraction, 16.5" x 8.25" wheel option, tilt, tach, vacuum, AM/FM, manual throttle...Dad ordered and purchased new 4/70. Currently frame off restoration in progress...
1972 Cheyenne Super 20 2WD, DK Blue/White, 90K ACT. miles, 402, TH400, 4.10 open, tilt, tach, vacuum, A/C, AM/FM, manual throttle.. A mostly original paint never rusted Texas survivor...
2017 Sierra 1500 SLT 4WD, Black, 41k miles, 5.3, 6L80E, 3.42 LS, 20" polished wheels, everything but moonroof and 6.2...
2019 Canyon SLT 4WD, White, 60k miles, 3.6, 8L45, 3.23 LS, 18" wheels