welcome to the Dark Side.
R60 on 900sqm would also yield eight 2x2s or ten 1x1s as apartments...which is kinda the point on the R60 zoning.
Have a look at Table 4 in the R Codes here > http://planning.wa.gov.au/dop_pub_pdf/State_Planning_Policy_3.1-Residential_Design_Codes.pdf
you will see...