I had some questions on this subject in the past and I thought I had all of the holes in my firewall figured out but I need to double check on one. People replied back and said that the factory oil sender hole through the firewall was 1/2" and right behind the distributor. I have a hole that is slightly larger that is behind the distributor but toward the passenger side of the car. Does anyone have any clear pics of the hole and or oil line going through it. I just ordered a ton of parts and I'm getting ready to start painting the firewall and putting the subframe with motor back together. Pics later. Thanks

The assembly manual has a page with the location of all standard holes, and location of dimples for locating holes for options.

The hole you describe might be for the speedometer cable on muncie 4 speed. For all others, it's on the outside of the booster.

Heres a picture of a 67 firewall. The rubber grommet is at about the 7 o'clock position from the windsheild wiper hole, just inside the edge of the transmission tunnel. The muncie speedometer hole (not punched out in this picture) is just below and to the right (looking at the picture)of the rubber grommet for the oil line.

http://www.sleepingfleet.com/graphics/firewall.JPG