Preview files in finder without quicklook
The plugin qlstephen does in fact show the content of text-based files in the preview pane, not only the QuickLook window.  What really threw me off was that the pop-up window &amp; the pane embedded in finder are both called QuickLook.

Anyway, it's dead easy to install.  Download the latest version from here: https://github.com/whomwah/qlstephen/releases

Unzip

Copy the binary to the directory ~/Library/QuickLook  (create QuickLook if it doesn't already exist)