hello,
as per revision nov 01/09 the MTOW of these aircraft are 73.5.
there is an SRM note that the certified MTOW at time of delivery is still valid as per this revision.this would change in the next revision if jetstar have offically changed the MTOW
jetstar could have a part 21 approved organisation to issue SB for MTOW change.
the highest WV of this model(covered by SRM) is 15 which has a MTOW of 78T.
hope this helps