This truck is literally a "barn find" for real. 28K original miles sat with 1/2 tank of gas for almost 35 years. I pulled the tank and replaced it, along with the pickup tube assembly and hoses, gauge sending unit, and new filter. Blew out lines at the tank connections all the way to the front, all good. Put gas in and it cranked up as soon as gas got to the carburetor. Running rough and found #3 & #4 dead. Checked fire, good. Checked compression , 180 across the board. Checked fire at the plugs with a spark tester, all good. Moved the plugs around and never changed a thing. Pulled the valve cover, everything as it should be. Checked for vacuum leaks, nothing. I'm 69 years old and been a mechanic for a very long time, but I have to admit I'm stumped. What am I missing?
If you confirmed spark, fuel and air, I'm at a loss too. You said you pulled the valve cover. Did you rotate the engine to make sure the intake valves were opening? I assumed they were if your compression checked out.