There is a sense that things are right in the world when things are just like they should be. One such instance is declaring an Arduino board that has not been done so yet.
Fortunately, the board is fairly similar to another board, so my work was minimal. But here is what I had to do:
Add a new JSON file for the board:
In this file I had to update some values like name and variant. Also, I double-checked the board hardware IDs, CPU, flash, and upload settings.
The variant name is used to find the additional files used by these boards. In my case, it is just one file, pins_arduino.h, which I added here:
Note the folder name matches the variant name from the JSON file before. The data for that file had to be verified by looking at the published specifications for the board.