No, they were simply available with or without stamping, this particular type anyway.
And yes, the mounts are riveted on originally, must be for a different setup or booster perhaps. Some of the fancy brands like Detroit Speed that make the brackets also have boosters with no brackets, various vehicle use and adapt.
You could adjust the angle and height of the booster by adding a washer or two to the top studs, you may not have much access. I had to do similar to mine as it's RHD converted and didn't have an angled mount on the firewall. I made a spacer plate now but testing with washers until 17 degrees. The booster mount makes it angle upwards while the firewall mount angles downwards just slightly.
Grab a pic if you can, might be easier than guessing what the scenarios could be for sake of conversation.