For those searching in the future,
I tried searching for ways to "ENTMAKE" a BOLD font. There are NO bit values or flags that need to be implemented. it is Entirely dependent on the font file name. In most cases the "xxx.ttf" extension (for True Type Font).
For those using windows, your true type fonts can be located in.. C:/Windows/Fonts
- Navigating to this location will open your fonts

- You can see that some of these contain multiple files (the stacked images). Double-click one to open its font types (bold/italic/narrow, etc..). In our case we will open Arial..

- When you see your desired font, right-click > properties and this will show your desired font name when trying to ENTMAKE..

- Thus, for our situation of "Arial Narrow Bold" we will use..
'(3 . "ArialNB.ttf")
Also, when all-else fails. THIS POST pointed out that using -STYLE you can merely add "Bold" to the end of your font name to weirdly set the font to bold. [e.g. (command "-STYLE" "MyStyle" "Arial Narrow Bold" "0" "1" "0" "N" "N" "N")]
Resource 1 - True Type Fonts
Resource 2 - STYLE
...hope this helps!
Best,
~DD