Factory Track width for '67 Chevelle with Disc Brakes????

[ZZ3ElCamino]

I am trying to figure out wheel backspacing for the front of my car ('67 El Camino) and right now it has drums. I have Baer's track kit with their hubs that mount to the factory spindle. I called them and they said that it will probably be ~3/4" wider than what it is with the drums, and .080" narrower than a factory disc brake car. Does anyone know what the factory backspacing and or track width was for a '67 Chevelle/El Camino with disc brakes?

[ZZ3ElCamino]

My thoughts were an 18 X 8.5, not sure about the backspacing yet. Any suggestions?