Tach wiring location

I have a customer that wants a tic-toc-tach installed in his '69 Charger. He has the two harnesses (engine and dash) for the tach. The dash harness has a 1" grommet on it where it is supposed to go thru the firewall.
Does anyone have a picture of the exact location where I have to put the hole? There are a couple of "dimples" up near where the headlamp vacuum harness comes thru. I'm presuming it must be near these. Thanks...

From a previous post:

referencing the above photo there should be a dimple in the firewall where that gromet is.

Yes..there is a dimple there...Thanks to all !!