Akro,
You beat me to it. I was amending my post as you posted. I think TSO 145 specs are related to aircraft with FMS, and 146 specs for stand alone GPS installs.
Also, I think I may have been confusing alternate requirements vs sole means capability.
However, it will soon be a moot point.
CAO 20.18
On and after 4 February 2016, an aircraft
(a) that is first registered before 6 February 2014; and
(b) that is engaged in RPT operations or charter operations under the I.F.R.; must carry at least all of the serviceable equipment mentioned in 1 of the following subparagraphs:
(c) at least 2 independent GNSS navigation equipments that meet paragraph 9D.9 standards;
(d) at least: (i) a single GNSS equipment that meets paragraph 9D.10 standards; and (ii) an ADF or a VOR navigation receiver that meets paragraph 9D.12 standards;
(e) a complete GNSS navigation installation that has been approved by CASA as capable of achieving RNP in accordance with CAO 20.91.
.