I still think it is the timing. I had exactly the same problem getting my truck to start. I fiddled and fumbled with it of and on for about a week, and it just wouldn't start. Once in a while I would get a little pop, but that was it. I finally used the triangle to line everything up and it started on the first try.
If you have the triangle use that.
I don't know a lot about these old trucks, and I am not a mechanic, so I don't claim to be an expert, but I do know that is what worked for me.
You say it was running when he got the truck, but not well. That makes me feel even stronger about using the triangle to set it up. If the former owner had the circle painted white and was using that to set the time, then he was using the wrong mark, and probably fiddled with it enough to get it to run a little.
Do you have a shop manual? There is an excellent section in there about setting up the distributor after it has been removed. Good luck. Allen
