Luckily I have them on my 58 but the springs that go on the end of them are just as hard to find. It's part of the emergency brake system. When you pull the parking brake in the cab it pulls the brake cable and lever at the back and with the help of that part pushes the brake out to the drum.
If you find an old rear in a junk yard you can get them.
Larry


58 gmc 100 with 350 sbc