Two Times Can't be a Coincidence...Dart not Firing

Way back, you mentioned that you thought the engine was worn because of oil on the spark plug. It looks normal to me. The tip is dry. Your spark plug sits in a removable aluminum tube (like a Hemi) and you can get oil down there and probably just got on the threads as you removed it. Next time you fool with the plugs, have a set of new rubber seals for the plug tubes. They are real cheap. Rockauto has most common parts for your engine cheap. If you do want to check if your engine has good compression without a gage, remove the oil fill cap while idling. If you don't feel puffing from the hole and out-gassing, your rings are probably fine. The PCV should actually be sucking a little air in. Also, turn over the engine by hand (key in pocket) by tugging on the fan belts. If you feel 3 strong "air springs" per rev (mark w/ chalk), your engine is probably excellent. Turn it clockwise (looking at it from the front), i.e. the crank should turn the same way you would turn a bolt. BTW, you can get a bolt to put in your crank and thus turn it over with a long socket wrench (I use a ratcheting clicky torque wrench from Harbor Freight).

Look at the engine idling at night in the dark. If you see faint flashes, that is arcing from the plug wires to ground and you need to change plug wires. That would be exacerbated by humid weather. The slant distributor is also subject to moisture where it sits low. My 69 slant wouldn't start on the Texas coast after a big rainstorm. The foreman sprayed WD-40 inside the distributor cap and it started right up. That was a gulf coast trick everybody but me seemed to know back then.