I like to mount mine on top of the dash in the drivers corner. I pull the bottom screw out of the a pillar trim and screw my mount to that hole, that way I don't have to drill or cut anything. Here is a link to a thread that shows a few different locations though. Good luck Justin.
http://www.forabodiesonly.com/mopar/showthread.php?t=16707&highlight=Tach+location
