Safe disc Thickness? Odd anti-rattle/ retainer set up

That's a 1965 pad retainer.
If i remember correctly from when i did lots of these brakes, minimum is either .780 or .790

Fine lines
Inline Tube.
Classic Tube.
And others, sell the hard lines.

And.
If you really want pad retainer clips like that, any Mustang restoration company that you can think of, will have retainers like that.