These brackets are needed on the ignition side of the engine to support the ignition coil rail. The 0331 head has threaded bosses on it to support the rail. The older heads don’t have them because those engines used distributors though.
Here are some pictures of what they look like along with a diagram showing how I used the the original screws and just installed them upside down.
You can buy a kit with two of these brackets from me here or make your own out of some thin aluminum flat stock.