On July 3, 2013, Mike Busch of Savvy Aviator fame, held an EAA webinar on engine leaning techniques, following up several other leaning sessions which are still available on the EAA website.
These are my notes from his talk, the most significant portion of which (to me) was his assertion that Lycoming now recommends mag timing at 20 degrees top dead center, rather than the 25 degrees recommended on -- in my case -- the data plate on the engine and the owners guide. My engine was purchased in 2008. We might be hearing more on this. Perhaps not.
The biggest impact on the way I've been leaning my engine, however, is I am now implored to stop using exhaust gas temperature to determine the peak. I've been making a big mistake. See the notes at the link for more.