Factory setting is 8 +/- 2 degrees at 1,600 RPM. Bear in mind, that was also with the EECU trimming spark. I too have seen that article (and most others) and it does say 8, but I think that's because that's what the factory said. My 258 won't run that retarded, I have to advance to about 12-15 if I want a decent idle, but right now my 258 isn't running at all, so that may tell you something
Definitely give the damper mark a dab of paint once you clean it up. It will help you with the timing light if you use one.