My 1971 Road runner

[Runcharger]

Likely a head gasket by the looks of the one plug, especially if you caught it right away. And yeah it's been running rich.

 

[71Beeper]

I agree the plugs are dark in color. The carb is a Holley 800cfm. That was the carb used when it was on the dyno. The primary jets in it are 72's - I'll jet it down to 68's.