I measured the Kohukohu remains as follows:
Gauge 3 ft 6 ins
Wheel diameter 2 ft 1.6 in
which differs a little from the figure of 2 ft 3 ins given previously
Wheelbase 4 ft 6 in
Looking at the wheel design I have little doubt that this locomotive is a Kitson similar to T53.
Further information and thoughts will be gladly received!
Robin Hoare, Rawene