Help needed for diagnosis - pictures inside

Simple questions:
1. The original post tells of a bad miss. Is this erratic idling or a strong miss on one cylinder?
2. Does it clear up with higher RPM's, like 1500-2000 RPM?
3. I see some crush on the plug rings, but are you tightening them to proper torque? I turn them 1/4 turn after lightly seating. (Cast iron heads.)

If it is a one cylinder miss, then after re-setting gaps, pull the plugs wires one at a time to ID the missing cylinder. The dirty plugs may be indicating one but you need to isolate it. Once isolated, then you can do the usual tests with tweaking the valve adjustments on that cylinder, checking for free valve movement, spraying WD40 at the intake runner for a leak, etc.

This can be a lot of things, so you're just gonna have to start eliminating possibilities.