Re: #1 plug...........clean with spark???
I'm confused about your question. Are you asking why is the spark plug still clean even when it appears to be burning fuel?
Your second question about idle speed being unaffected by a disabled plug might be answered by the amount of rotating mass in a 468. The torque from the other seven cylinders can compensate for the loss of one spark plug at idle.
1970 Chevelle Malibu purchased new in 1970
355 SBC, XE262H cam, Performer RPM heads, MSD HEI, TH200-4R trans, 3.55:1 Posi, digital gauges, QA1 coilovers