Those are SURE-STOP-EQUALIZERS! Sacramento Vintage may still sell them??
Minerva had them & they worked VERY WELL!----I "think" they help apply MORE pressure than stock!--YES, you gotta' keep your brakes adjusted, so they don't "possibly" pop over center, BUT you're supposed to that REGULARLY anyhow!
IF you use them, be SURE to shorten the operating pins, per instructions. "Someone" DIDN'T do that on Minerva & had the front rods adjusted to where they were on by only "about" 2 or 3 threads (EEEEK!)
Bill Screech