The "correct" timing is now not published because the engine is no longer stock. when I did my 3.4, I hooked up a scan tool and watched the data list while I drove it. Look at knock sensor activity, set the timing so that the knock sensor only retards the timing under low speed high load conditions. Basically you want as much spark advance as you can without pinging or detonation. also use your fuel economy as a guide. As you approach the ideal timing advance your fuel economy gets better until it is too advanced where it drops significantly. The Knock sensor will of course hide this to a degree by retarding the timing in over advanced situations.