There are numerous ways to lash valves in an engine. I prefer the firing order method because it works with any camshaft type. The firing order method allows you to lash the valves on an engine stand or with the engine in the vehicle and not have to readjust them again.
SBC firing order: 1-8-4-3-6-5-7-2

STEP #1
Find top dead center for piston # 1:
Many people think that if the timing pointer lines up with the TDC balancer mark that this is TDC #1. That mark could be TDC #6. This is because there are 720 degrees crankshaft rotation in one complete firing sequence. There are two ways to find TDC #1 first is by pulling the #1 spark plug, holding your finger over the hole and turning the crankshaft until it tries to blow your finger away, then once the timing mark comes up this will be TDC #1. The other method requires the valve cover or intake to be off. You can look at the lifters or rockers of #1 and #6 cylinders. When #1 is at TDC, #6 will have both valves open slightly. If you move the balancer timing mark to each side of the timing pointer, you should see both lifters or rockers of #6 moving up and down and #1 should remain stationary. If it is vice versa then you are on TDC #6 and need to move the crankshaft 360 degrees or one full turn.

STEP #2
Adjust the the lash of #1 cylinder:
While you turn the nut down jiggle the pushrod up and down. When the play just stops go 1/2 turn more. You need to make sure to stop when the pushrod just quits moving up and down, then 1/2 turn more on both the exhaust and intake valves.

STEP #3
Turn the crankshaft clockwise 90 degrees:
The easiest way to tell if you have went 90 degrees is with a balancer with degreed timing marks. You can make your own marks if the balancer is off the engine. Just measure the diameter of the balancer (from one side to the other) and then multiply that by 3.14 (pi) to find the circumference, then divide by 4. Example: Balancer measures 8 inches, which would be 8 x 3.14 = 25.12. Then divide this number by 4, which would be 25.12/4 = 6.28 (or real close to 6.25 inches). Then you can lay it off starting at original timing mark and scribe some marks at the distance you came up with. You can also buy timing tape and install it but the only thing is it won't stay on for very long. A total waste of money to me. Anyway, turn the crankshaft 90 degrees to the next mark on the balancer for the cylinder in the firing order, cylinder #8. Repeat Step #2.

STEP #4
Continue adjusting:
Keep turning the crank in 90 degree increments and lashing the valves for each cylinder in the firing order until all the cylinders have been adjusted. Remember, the firing order is 18436572. Do #1, then #8, so on and so on until done. When finished with the last cylinder, you should have to turn the crank one more 90 degree turn and you will be back on #1 TDC.

Happy Motoring,
Mike