Hooking up an OEM rallye tach

I doubt the wiring is even in a non-tach car

You have a factory service manual? Down load one:

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download

Page 8-149. Theres a wire green/ yellow trace goes from the tack out through a separate firewall grommet to the engine compartment, and ends up at coil -- and a separate dark blue which connects down at the fuse block which feeds the tach

On the Barracuda diagram they show the feed coming off one side of the turn sig. flasher