Adding fonts to your windows is, as you can see, easily done. The number and kinds of fonts available is staggering.
You should be able to find just about anything you wish, just Google "free fonts"
one example: http://www.1001freefonts.com/sfonts93.php gives you a major group of stencil fonts.
As to the "which to use" question, if your don't have a specific photo reference to go by, then any that look correct to you should be OK.
I'm vaguely sure that long ago as a youngster, I learned that different companies, during WWII, used various sizes and types stencils (ie Boeing had lots of different stencil plates in their salvage sales lot -wish I knew then etc.etc., but as a young boy I didn't think anything about it, but "thats neat".)