You can adjust them with out going through the firing order, but it is easy to miss a valve or two so I wouldn't recommend doing it that way.
To do it properly...
1. take manifold and valve covers off.
2. turn crank until cylinder #1 is at TOP DEAD CENTER
- both intake and exhast valves should be closed completly.
- if you turn the crank clock wise the #1 piston will go down, and when it starts to come back up the exhast valve will open, this is how I checked to make sure each piston was @ TOP DEAD CENTER.
3. while twisting the push rod tighten down the rocker arm nut, when the push rod doesn't turn easily any more tighten the nut 1/2 turn more, and you are done with that cylinder.
4. Continue doing this by following the firing order.
Make sure to double check your work.
Do not get the rocker nuts to tight or you will create a whole slew of problems such as floating valves, possibly destroying your lifters, and maybe even wiping(flatening) a lobe on your cam.
Good luck!
Cody