Below is the text from GM Service manual for 1997 Chevrolet C Pickup 5.0L, 5.7L, and 7.4L Accordind to this you don't set the timing but the timing offset. You need a "Scan Tool" that plugs into the truck and can read the data from the trucks computer. Besides from that, it looks like a normal timing procedure. You might be able to borrow a scan tool from a parts store, or at least use their tool and do it in their parking lot. Setting Timing Camshaft Retard Offset Test The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following: With the ignition OFF, install a scan tool to the DLC. Start the engine and bring to normal operating temperature. Important Cam Retard Offset reading will not be accurate below 1000 RPM Increase engine speed to 1000 RPM. Monitor the Cam Retard Offset. If the Cam Retard indicates a value of 0° ± 2°, the distributor is properly adjusted. If the Cam Retard does not indicate 0° ± 2°, the distributor must be adjusted. Adjusting Camshaft Retard Offset With the engine OFF, slightly loosen the distributor hold down bolt. Important: Cam Retard Offset reading will not be accurate below 1000 RPM Start the engine and raise engine speed to 1000 RPM. Using a scan tool monitor Cam Retard Offset. Rotate the distributor as follows: To compensate for a negative reading, rotate the distributor in the counterclockwise direction. To compensate for a positive reading, rotate the distributor in the clockwise direction. Repeat step 4 until 0° ±2° is obtained. Turn the ignition OFF. Tighten the distributor hold-down bolt to 3N·m(25 lb. ft.). Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset.

If you have the timing right the error code will remain cleared after you clear it with the code reader.