Well that's definitely true, I know for a fact the 70-72 calipers can be used with a 73+ caliper bracket because the 11.75" caliper brackets weren't around for 70-72, they're like 76-79. But there's a pretty good chance I reused the pins I had too, I just can't remember because I did that swap like 15 years ago. I do not recall having to search out new pins with a different diameter thread though, and that's the kind of detail I usually remember.
What you NEED to do is figure out the thread size/pitch for the caliper brackets you have. Because quite frankly I can't tell from your pictures if the threads are any good, and I definitely couldn't tell you if they've been re-threaded at some point.
The '70-72 pins are listed at 3/8-24, so perhaps you can confirm what your caliper brackets are?