The plane used by Jebediah (Bruce Spence) is a Transavia agricultural/survey craft, which is unique to Australia. For some more info on these planes, you might try http://www.monarch.net.nz/uplift/ or http://www.austehc.unimelb.edu.au/tia/503.html#2073. A better page is probably http://www.terravista.pt/meco/1121/airtruk.htm, providing you can read Portugese. For further information try a search engine like Google, you'll probably have the most luck by searching on the designer's name, Luigi Pellarini.