HI just installed the NGK ZFR5n's in my 74 Slant. I removed the gaskets, but I noticed the base of the plugs was more narrow. Does that counterbore stop the more narrow plug?
Yes; the only practical difference is the hex size (what size socket you need to remove/install).
the plugs tightened to about 20 ft lbs. and then loosened up almost like they were stripping ( or breaking through the tube) but then tightened up properly
