Unfortunately, the TAG 125 classes chapter, Chapter 44 in the 2006 Manual omits 2 included engines, the ARC 125cc (Typhoon) and the Sonik 125cc (when its homologated).

For everyone who keeps asking me, yes, you can use an ARC125cc Typhoon on an AKA track and yes, you can turn up and enter any offered TAG 125 class with one and you can't be denied or disqualified.  If in doubt, just ask Mr. Farley what happened when Paul Laskazewski used an engine that was approved for the class but had been omitted from the manual.  It's not a problem.  If the NKC have approved it, it's legal.  AMSAC said so.

Obviously an addendum should be issued to make sure there's no recurrence of the problem described above and you need not take my word for it, here is the relevant section from the TAG 125 rules put to the NKC and the NKC's unanimous minute approving them. 

NKC Meeting Minutes
General business from late correspondence:
1. Quade bikes Correspondence accepted
MOVED: NSW SECOND: QLD
VOTING: UNANIMIOUS

2. TAG regulations proposal:
Change the engagement of the clutch to 3000rpm
Homologation of the Sonik 125cc to take place before use.

Engines .
A variety of TAG (Touch and Go) style engines are eligible for use in this category. Engines can be added or removed at any time by the class promoter. Current Eligible engines are:-
1) Biland SA-250
2) PRD Fireball 125cc
3) Rotax Max 125cc
4) Parilla Leopard 125cc
5) ARC 125cc
6) Sonik 125cc

MOVED: QLD - SECOND: WA
VOTING: UNANIMIOUS