ticking not fixed by valve adjustment

You may have a sticking valve, or lifter, or bent valve stem, or something else… hard to know without being there to look, listen, and perform a few tests such as compression, vacuum readings.

As to the explosion at #5, probably carburetor leaked raw gas into intake runner pudding at back side of intake valve when closed, when that valve opened dumped raw fuel into combustion chamber wet the plug causing a miss-fire, and ran into exhaust where it finally lit off from hot exhaust flow and extra oxygen left from #5 miss-fire. There may have been enough fuel to cause a slight hydro lock condition; this is all speculation.

Anytime raw fuel enters a cylinder in any volume it can cause things to bend, and or destroy exhaust systems. Perhaps with fuel filled combustion chamber and intake valve trying to open while held closed by fuel, push rod was weak link and bent.