They look like they might be mounts for Jeay brakes. These were cam-actuated and came with m6 stud/bolts. The thing that doesn't make sense for Jeay brakes is that your mounts have holes for the springs, and Jeay brakes didn't use that kind of spring. But could be something like this. There were lots of little French brands of brakes that used m6 stud-bolts instead of studs on the frame.
If you reckon they might work, they are still cheap enough on ebay, not being associated with the dread RH.