6 cylinder tach wire firewall hole location

[Dirt's72]

I am installing a 6 cylinder tach in my 72 using an original tach wiring harness which came from an 8 cylinder 72 big block truck. I'll be using it with a 250 inline 6 points distributor. I know where the correct hole in the firewall is for the 8 cylinder. My question is where is the correct place where a hole would be in the firewall to a 6 cylinder? The brown wire does not look long enough to reach the coil if using the 8 cylinder hole location. Also do I hook the brown wire to the negative side of the distributor or coil? Thanks