Everything in Japan other than the Shinkansen high speed trains and some electric lines is 42 inch gauge. So Japanese protoype steam is all 42" gauge.
Z scale track actually scales out to 41" in N scale, so it is closer to Nn3.5 (42") than Nn3 (36").
Kiwis use TT scale (1:120) models running on N gauge track, which comes out to 42 and 3/8 inches in TT. PDC.
Your choice.