[awhtx]

It sounds to me like your carb is going "lean" when you try to accelerate. Carbs have an accelerator pump that squirts extra fuel into the manifold when the gas pedal is pushed down. This extra squirt of gas helps the engine rev up. When the engine tries to accelerate without the extra fuel the lean condition causes the engine to backfire. The gassy smell, poor mileage and backfiring indicate that you need a complete carb overhaul.

Your balancer surely has timing marks on it and they are hidden by oil or paint. Go under the car with a wire brush, a can of carb cleaner and a ratchet with a 15/16" socket. Put the ratchet and socket on the bolt in the center of the crankshaft pulley. Clean the portion of the balancer you can see. If no timing marks appear rotate the crankshaft with the ratchet and continue to clean until you find the timing marks.

 

[awhtx]

If the timing chain has jumped 1 tooth the engine will not run with the timing set at 10* or 12* BTC.
The timing chain in my '69 Mach 1 jumped 1 tooth causing the engine to die and I had to reset the timing to get it started again. A few days later it jumped another tooth and resetting the timing would not get it started. I was forced to replace the nylon tooth cam gear that had worn teeth.

 

[awhtx]

The yellow spark indicates weak ignition. It should be blue, look like a lightning bolt and jump across a minimum of a 3/16" gap.