Well, I got home tonight, and looked a little more, and have a little more info.
The back two plugs, on both sides are dark. The front two plugs are half white and half chocolate. On the passenger side, #2 and 4, the white is much more pronounced than on the driver side, number 1 and 3.
Also, while letting it run, the headers turn glowing red hot at the point where the four tubes gather, right above the collector. Sanderson (the header mfgr) tells me this is absolutely not normal, and their first thought was the engine was very rich.
I would buy this, as I had overjetted the carb when the symptpoms of lean drivability started, and based on teh back plugs.
I am about to decide that I have blown the head gasgets between the cylinders.
As for why that would happen: this engine has a small B&M Holley Street blower on it, and I got on it pretty hard recently.
I would prefer to have a way to validate that the head gaskets are blown before pulling the engine apart. I may call Holley and discuss this with them tomorrow. I don't know if it is possible to blow head gaskets and not have symptoms of water in oil or something like that.