A 59A engine, and if still stock, has a pancake ignition mounted on the timing cover. The first thing to do is to look at the distributor cap for cracks (even new!!) as splashed up water will cause a cross fire. Then there are those @#$% metal spark plug looms (or as Ford called them, "conduits') which were/are notorious for causing cross fires at the spark plug. Many folks back in that period removed them and ran the wires free of those gadgets. That snapping noise you hear is possibly a crossfire inside that RHS loom. As far as a 1/4" spark - that sounds good, but cross firing will usually only happen under load. 110 psig is fine and within the high end of limits as 120 psig is spec.