Will the engine run if you take all 3 of those plugs off at the same time?
I had this happen to me once on a 270 gmc 6. Turns out I wired it in reverse rotation. For 3 weeks my truck ran like crap, but it was still able to make freeway speeds. I could pull 3 wires at the same time and no difference in the way it would run.
Check Rotation First. 1-5-3-6-2-4 CLOCKWISE!
If you have any doubt about the ignition system, change cap, rotor, points and condensor, plugs, and wires. You may also need to change the coil. I believe the points that are available today are of inferior quality and would reccomend eliminating them by using a pertronics ignition. However the symptoms described do not make the ignition suspect.
If you want to check the engine on the cheap without spending much money, Pull the spark plugs and examine each one. Are they wet, oily, ashy? They can tell you a lot about whats going on with an engine.
Pull the valve cover, are all the rockers adjusted properly? Are all the rockers moving? It is very common for engines that have sat a while to stick a valve,or three and cause the pushrods to bend. This may be the cause of your problems. You might not need an engine build to fix it. You can remove the bent pushrods and straigten them with a hammer on a wood block, or concrete driveway. You can unstick the valves by tapping on them gently with a hammer on a block of wood.
Anyway report back to us with your findings
