Speedometer Cable?
 

The car didn't have a cable from the speedometer when I bought it. I'm not sure where it should run through the firewall. Took some pictures of likely areas.
There's a fairly large diameter hole behind the brake pedal:
http://chevelleforum.org/picture.php...pictureid=4790
There's a small hole in the center of the firewall:
http://chevelleforum.org/picture.php...pictureid=4793
And there's an access below the throttle cable:
http://chevelleforum.org/picture.php...pictureid=4792
Can anyone help out?

Your pictures are too small to really see anything. I'll take a look at mine this morning and let you know.

I think it depends on what model it is sometimes. Mine is the one behind the brake.

Mine, a 70, comes out almost directly below steering column. Just below where firewall curves back into floor pan. Goes through a plastic/rubber grommet that pops into sheet metal.

That's the one behind the brake. Sorry about the pictures, they looked fine in my gallery but showed up small in the post.

My car is covered so I only looked under the hood, not inside. I believe there is a plastic kick plate at the top of the carpet that the cable passes through.