Select font when converting .txt to .pdf from command line
The solution is to create an afm version of the font you want to use which is American-typewriter for the enscript program to create with. 

What you need to do is grab a copy of the  AmericanTypewriter font. Which is located at /Library/Fonts/AmericanTypewriter.ttc

Next obtain and run the program ttf2pt1.  Copy the output file that you can name atw.afm to enscript's afm directory located at /usr/share/enscript/afm.

Edit the "font.map" file located in /usr/share/enscript/afm

Add in the AmericanTypewriter font to the list.

AmericanTypewriter         atw
AvantGarde-Demi            agd
...                        ...


Lastly re-run the enscript and choose the new font, process as you would normally after that but now including the AmericanTypewriter font.

enscript -f "AmericanTypewriter12" -p postScriptOutputfile yourFile.txt