Are these bricks old LEGO/Duplo clones?
As suggested by @mindstormsboi I contacted LEGO customer services and sent them a link to this question as well as many additional photos.  The information was passed to their expert team and the answer that came back was &quot;they believe that these are not LEGO® parts&quot;. They were not able to identify them as a known clone type. I feel obliged to accept that as a definite answer, although it leaves unknown who actually manufactured the bricks I have.  I will continue research into that question, but elsewhere.
The customer service team member also gave me two interesting links to a fan created website with some of the history of LEGO parts, as well as section covering many of the clones and similar brick building sets.  I include the two links below, as they may be of interest to some who find this question and answer.
https://www.inverso.pt/legos/
https://www.inverso.pt/legos/clones/texts/mobitec.htm
Thank you to all who contributed their knowledge, experience or point of view.