For the 2nd stamp you need to check for Chad in your Scott index.
It is SG19(1924), originally a stamp of Middle Congo, colours changed, overprinted TCHAD, and further overprinted Afrique Equatoriale Francaise.
For the Australian Customs Duty stamp, check out this site for more information than you would ever need:
http://www.ozrevenues.com/Revenue-R...atalogue.htm