The pilot had been cleared to transit the Coolangatta control zone southbound at 2000 feet. He was instructed to remain east of the coast and to report abeam Jupiters Casino. The pilot subsequently reported abeam the Coolangatta Control Tower, and was instructed to report again at Hastings Point which is the southern boundary of the control zone. A Bandierante aircraft inbound to Coolangatta was descending through 2200 feet, about seven miles south of the airport, when the crew saw a Cessna on a reciprocal heading pass below the right wing. The pilot of the Cessna had not complied with the instruction to remain over water, and passed in close proximity to the opposite direction traffic. The pilot of the Cessna did not see the Bandierante, and said that the radio was difficult to understand as his headphones were not compatible with radio. The Cessna was on a ferry flight to Tasmania, and the pilot who was 79 years of age said he was not familiar with Coolangatta airspace.