I have an idea that few people know about. Since you bought the truck from someone else there is always the posiblily there are differenct than stock cam and other parts. If you have a timing light I would check your current timing, and check to see that the timing is advancing on the vibration damper. Then buy a vacuum gauge and try this.
If you have points, set them to 30 degrees, with a dwell meter.
Adjust the idle screws on the carb so that it runs the best and adjust to the factory idle speed.
Connect vacuum gauge to an outlet on the intake manifold.
Turn the distributor until you get the highest reading.
Then turn the distributor back the other way so that it reads one less. If your max reading was 20, turn the distributor until the vacuum gauge reads 19.
I have 4 cars that I have timed this way and it works great as long as your advance is working like it should.
Let us know if it works for you.