Adjusting valves after head gasket replacement

I've just replaced the head and lower manifold gaskets on my 96 sierra. The Chilton book says to adjust valve lash by turning the motor to 0 degrees on the timing mark to begin adjustment. My sierra doesn't have any timing marks since the timing is not adjustable. Can anyone help?

Find the lowest point on the cam lobes on each cylinder by watching the pusrod movement, bring the rocker down to just eliminate the lash, do this on all 8, fire it up and now you can properly adjust them by loosening each rocker till the valve clicks then down till it just stops plus 3/4 turn, but check the specs some are one turn. There is an easier way with degreed damper or distributor.