The engines #1 cylinder is the front cylinder on the PORT side of the engine.
There is a method for locating the #1 cylinder spark plug wire pole of the distributor cap.
Remove all the spark plugs.
Use a good socket wrench which will fit the main pulley bolt in the center
of the harmonic balancer. A long breaker bar is good as you will need some leverage to turn the motor by hand.
As you face the front of the motor, gently turn the wrench/pulley as to turn the motor.
While you have someone turn the motor by hand, stick your finger into the #1 spark plug hole. Eventually you will feel the compression start to build up against your finger.
Observe the balancer once you start to feel compression and look for a timing mark/line scribed into the harmonic balancer. Also locate and the Timing Pointer which is mounted to the time chain cover. The deepest mark on the Timing Pointer is going to be the TDC (Top Dead Center) mark.
The idea here is to line up the scribe/line mark on the harmonic balancer with the center of the deep notch on the Timing Pointer gauge while the piston is coming up on its compression stroke.
Once you have that line directly lined up with the zero degree (deep notch) on the pointing pointer you are at TDC (Top Dead Center).
Now..... remove your distributer cap and see which plug pole the rotor is pointing.
I like to scratch a mark on the side of the distributor housing exactly inline with were the rotor is pointing. In case you didn't know... the rotor is the piece on the distributor shaft which turns when the engine turns. It "distributes" the spark from one pole to the next.
The pole on the cap to which the rotor is pointing is going to be your #1 cylinder.
Mark the cap so you will always know which pole is for the #1 cylinder.
Your firing order is 1-8-4-3-6-5-7-2.
All standard rotation GM engines have a clockwise rotating distributor shaft.
So... as you view your cap from above, the correct plug wire order is 1-8-4-3-6-5-7-2 in the clockwise direction.
Note: The port side of your engine cylinder numbers start at the front as 1-3-5-7
The starboard side is 2-4-6-8
Take special care to make sure you get your firing order correct.
Reinstall your spark plugs and hook up all the plug wires.
Now, check again to make sure you have the correct firing order.
This is the most common mistake.