So after a few hours with Gemini I think I got it. Here is how Dyckman files need to be organized and named to load properly without manual intervention.
The era_ballparks.txt file (last column) needs to read "Dykeman_Oval".
The Textures folder, just in case, was renamed "Dykeman_Oval_Textures"
The .mtl was opened in Notepad and, after finding and replacing all the file location references to match the new texture folder, was resaved as Dykeman_Oval.mtl.
The Dykeman.obj file was opened in Blender and resaved as "Dykeman_Oval.obj"
The .prk file was regenerated in the Bark Profile page (export this park's data to a file" after I linked to the new .obj file via the Pictures & Coordinates tab in the Ballpark editor.
Note I synched the capitalization too to remove that variable.
The old Dykeman.ootp3d file was deleted and the I let the game regenerate it after I started the game over and advanced to see if the park would auto-load. When it did (yay!) a new file was indeed generated.
I can see I am going to have several parks to dig into today. My hope is that the next time someone googles what's wrong this can be a guide on how to troubleshoot it. And to my modding friends, please keep the same name on those key files!
