Thank you for your response. Some things have worked; others have not.
I was able to Override Content and have the 4 selected posts display in the instance – great!
1. Despite testing several configurations of Content Options > Formatting Options, the content still does not appear on two of the posts, only the title. I have not yet tried creating custom content for these posts, but perhaps the answer.
2. When I have the Output Options > Show the plugin under content > ON, then the instance appears on each page and displays the correct 4 posts. However, when I turn this setting to OFF, and then add the instance shortcode to the page: https://www.surroundslandscaping.com/dlm-test/ the result is that only blank white boxes appear, with no content at all… no image, no title, no content. You'll can see that live at that URL.
3. While I was testing the various settings I got several white screens of death. Hmmm.