This is what we call "bag of worms". I can confirm the thread pitch; no problem. It's just the pins for 73 are not available per my searching. Thanks for your comments and appreciate the help.
Right, but it doesn’t matter, you still have to figure out what you have, because it may not be right regardless of the year.
And to that end, I remembered that I have a ‘73 C-body spindle and brake caliper bracket set up, because it’s a 1 year only deal for C body brake conversions. And I have the pins, which are the same as the B/E body pins.
And I can confirm they are the same exact 3/8-24 that the 70-72 pins are advertised as.
Which leave us with, what threads do your caliper brackets have?