i have no spark on cylinders 5 and 6 ford 4.9L 1987. what are possible problems?

What is your question?

I have a 1987 Ford E250 4.9L 6 cylinder with no spark misfire. I tested for spark off the distributor cap post. No spark for cylinders 5 and 6. I adjusted timing 60 degrees forward and moved wires forward, miss moved to cylinders 1 and 3. I changed distributor and set to original timing, the miss persisted on 5 and 6. New wires, plugs, cap, rotor, two different distributors and problem persist. do you have any suggestions?