if its running it cant be THAT far out. crawl up under it with a rag and wipe the damper off really well. You are looking for a bunch of marks and numbers called a degree wheel. Once you find BTDC 10, draw a line on it with a white or yellow paint pen (just mark in the groove).
You will then pull the plug from the spout connector. its a little plug (dead ends, and a jumper pulls out of it) that branches off near your distributor. start the truck, and put a timing light on it. rotate distributor until the line you drew is hitting your timing needle.
tighten distributor, reinsert spout plug.