I have one 80 that runs like a champ, the other is acting a fool. With fresh gas, a new carb and fresh pipe and a header, the engine is just not moving the truck. I highly doubt its the gearing, should be 4:10's. Long story short, a friend of mine mentioned advancing the timing to deal with the quality of modern gas in such an old engine......any other thoughts? I can believe its the timing, but i fear the worst....it happens.

 

Timing can be "too advanced", maybe he left the bolt loose on the dist and it moved out of timing a big. If you guys worked on the valves any and over tighten them you can get the same problem as well. Have you taken the valve cover off and checked the chain?