Timing Based On Which Year?

these old sixes like a lot of timing. remember that 1968 is the year the first clean air act took effect nationwide, so automakers backed the timing down on their cars to meet emission standards. us six cylinder guys like 12-14 degrees initial timing, sometimes even more.

one bit of information for you, the balancers on these engines have a tendency to slip over time and the timing marks then become inaccurate. you can however "power time" the engine. you advance the timing until you get detonation, then back the timing down until it stops.