Total Brake Job on '70 Dart

You don't need nos Mopar. In that eBay suggestion look for old stock from what I call the "big 3" in brake parts/ those being bendix (who was the oe supplier back then) Wagner and raybestos.
Even back then they had "good " (cheap grade) "better" and *best".
Other companies that are gone now like EIS (who supplied car quest for years, then raybestos took over right up until Advance bought them out) had a good product as well. Any of them made wheel cylinders, hardware etc. Also there's Carlson who did hardware and wheel cylinders, caliper rebuild kits, etc but not pads/shoes.
I am always scouting eBay for parts like these that fit my junk, and "stock up" when I find a deal.

You're right though today's stock is questionable at best/on parts that should never be in question.
I hate buying house brands of brake and suspension parts, the 2 most important systems on a car. With house brands, you have no idea what you're getting.
I always try to get name brand whenever possible unleash I'm in some kind of a bind and have to have something "now" and even then I'm keeping it in the back of my mind that these parts may not last all that long. I mean, ask the counter help "who made these"
Anyone with 1/2 a brain knows there is no "duralast" or "brake best" factory.