I normally find/see those retained by screws don't know that I've ever seen one where the brackets are riveted in place as your pictures show. Wonder if this was a repair from the past.
The brackets/blocks on your examples are on the inside of front of the headlight bucket where typically originals are on the back side. Looked through my library and looking at the examples I have (stopped after 100 of them) the brackets installed on the back side with Phillips head screws with flat ends (not pointed). This does make the most sense considering the raised thread bosses on the front face surface at the cut out. The examples were from all three plants.
Some examples the ones I found
Did have a pair of 69 head light buckets handy in the back of the trunk that I snapped a couple of pictures of and I believe they are both service replacements based on a couple of clues. Those brackets/blocks were installed to the front side like your but used Phillips head screws with pointed ends. Would show pictures of those but it might lead others in the wrong direction at this point in the discussion