Don't have a template but I can recommend you go thicker than 1/4" unless all you want is a thin "aesthetic" panel. Mounting anything in 1/4" will be not very strong. Used 5/8" when I did mine out of particleboard, other guys have used MDF. See link below for pictures of my panels.
Do you not have the original ones or did your truck not come with the panels?
<font color=orange>'79 - 406 TPI -<font color=orange> K5#5 - <font color=blue>See it at---><A target="_blank" HREF=http://www.blazzinor.coloradok5.com>http://www.blazzinor.coloradok5.com</A>