The pilot stated that the right engine quit after landing at the Wichita Falls, Texas airport. A witness stated that he attempted to start the engine several times when the right wing exploded during the last attempted engine restart. Damage was concentrated in the right wing between the engine nacelle and the main fuel tank. There was no fire associated with the explosion. Examination of the wreckage indicated that the explosion originated at the engine area and had emanated from within the wing. The pilot indicated that he had taken off on the main fuel tanks and then switched to the aux tanks during the flight. Before landing, he had switched back to the main tanks. According to the FAA inspector at the scene, the main fuel tanks were found 'overfilled beyond the filler openings.' The pilot operating handbook requires substantial operating time on main tanks prior to switching to aux tanks. The overflow from engines returns to the main tanks only.