340 ignition timing.

Yes-that's a decent method for getting the best idle, but you also have to consider the timing curve...unless you're running a purposed engine with locked timing, 34 is too much initial...it'll wind up somewhere north of 50 degrees when it's all in-and that'll end up hurting parts.

Since you have the light on it though, map out your curve like these guys are saying and see how it drives, then modify as necessary to get best performance and drivability.