Here you go, Taken from QLD transport modifications guidelines:
Vehicles that are required to comply with ADR 69/.. or
ADR 73/.. or where originally fitted with a driver airbag
must not be fitted with a replacement steering wheel
without an airbag, unless it is supplied by the vehicle
manufacturer as an option for that model.
The diameter of any replacement wheel may be up to
25mm smaller than the original wheel but must not
be less than 350mm.
I'm pretty sure its illegal alltogether to have a momo wheel w/o airbag on a GTT as they came standard with airbags.