Quote:
You can not 'bore out' a 1200/ A12 engine to 1500cc as it would need a bore size of 82.5mm [from 73mm] & I don't think that the end pairs of bores are spaced that far apart [center to center]
Have a look at the engine number. The prefix [A12, A14, A15] should tell you what the core engine is.

Do you know what features in a gearbox you want?
Do you want direct in fifth, or overdrive?
Do you want a standard shift pattern or dogleg pattern?
Do you want a light sport box,[56A] a heavy duty box,[60A] or a super heavy duty box?[63 series]
Do you need the original cable clutch operation, or do you have the facilities to engineer a hydraulic clutch operation?

Lots of choices here in Datsunland, but it would be a good idea to know just what it is you are seeking & why.

If you have an A15 powered Ute with the original diff, then I suspect that a 60 series overdrive box with conventional shift pattern & cable clutch operation would best suit your needs, but be warned, they are not cheap.

Question to the gearbox experts.
Is the 60 series four speed gearbox case [bellhousing] interchangeable with the five speed one? If so, then US five speeds with hydraulic clutch systems could be converted with a junk four speed donor box over here.