Is there a QuickLook preview for plain-text files with unknown extensions? A similar question was asked here but the answer refers to something called QL Stephen, which only claims to preview files with no extension.  I need something that will show previews of files with extensions that are unknown to the Finder.  They are all plain-text files.  And, it needs to run on Lion (10.7).

To clarify: I'm not looking for a default QL for any unknown extension, but rather for one that will preview certain specific extensions (e.g., .sps, .fort) as plain text.
You can use QuicklookStephen (https://github.com/whomwah/qlstephen).
Install via Brew:

brew cask install qlstephen


and then reset the Quicklook plugins:

qlmanage -r


and you should be good to go!

Tested with both files without extension and files with "unknown" extension (e.g. .nfo)