OK, got it working. Thank you garlin for pressing forward with this.
Here is what the issue was;
<tldr>
You have to manually extract (7-zip) the OEM ISO to a folder on your desktop/laptop before 'Adding' the OS files to NTLite (Add>Image directory, not Add>Image (ISO, WIM, ESD, SWM)) so that the correct 'sources' folder is available/exposed.
</tldr>
Although NTLite will ingest the raw (compressed) OEM ISO and do all the things, only by manually extracting the OEM ISO first, will you expose the needed 'sources' folder that the other threads reference.
To add to the confusion, the two folders under "Boot/Setup" in the NTLite interface each have a 'sources' folder (only visible in NTLite), but those will not work for this activity.
Once the correct 'sources' folder is available, you can then start creating the $OEM$\$1\<more folders here> folder structure to meet your needs.