Well, I went ahead and used finger tight plus 1/2 turn since these are gasket seat spark plugs. As far as the gap, I found 0.044 on the NGK site. The existing plugs I measured to be about 0.055. The new ones were supposed to be pre-gapped but they all measured about 0.040 by my gauge. I installed them as they were, without re-gapping. Cranked it up when I finished and the car still runs about the same.
I didn't read the codes again but I imagine they are about the same, too. Can't say that I'm really surprised.
Wasn't able to see much concerning a possible gasket vacuum leak. All plug wells were clean & dry except No. 4, which was sopping with oil, but the oil wasn't high enough to reach the boot of the coil. The coil was clean & dry. No oil on the tip side of the plug (in combustion chamber). I'll post a photo later of the plugs after removal. Nos. 1, 2, 3, & 5 were black, with No. 2 being a little less so than the others. Nos. 4 & 6 were much whiter.
Guess I have to figure out now how to identify a vacuum leak, or just take a chance ripping the valve cover off for exploratory surgery.
