1979 Dodge Van darn thing won't start

My van was converted to an Ice Cream truck then run by a guy with little mechanical maintenance for several years. It was in bad need of a tune up and then stopped starting yesterday. Cranks fine, won't catch. Changed plugs and wires and found no spark. Changed coil, good spark and good fuel flow. Still not catching. Changed rotor and distributor cap. Tried to catch once on the first try but not catching at all since then despite several attempts and triple checking all the connections. I'm outta ideas and looking for suggestions. I also changed the ignition resistor, partly because a neighbor suggested it and mostly because the previous owner had a spare in the glove box. I find anything he had a spare for tends to go bad regularly.