The trick to re-alligning the distributor is to wait until the second valve from the front on the drivers side (number one intake) closes and continue rotating until you hit TDC. Here you can see the valve starting to open:
The intake valve is opening to let gas/air mixture in. When it closes, all of the gas/air has been sucked into the cylinder. The piston then starts compressing the gas/air. The spark to the number one plug has to ignite the mixture just after the piston starts coming down.
Keep on rotating until the timing marks show top dead center:
The rotor should be 1/8 of a turn counter-clockwise from straight forward to the front of the truck.
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