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I went to the nissanforum site, found your thread & read the whole 15 pages. Quite a story & I loved it.

Nowhere in the whole story did I find any of the Justy pistons that were bigger than 79mm, & it looks like it was necessary to deck the block to use them. This gives a displacement of 1608cc
To get a displacement of 1675cc requires a bore size of 80.65mm which is another 1.65mm or .066 thou. bigger again.

Mazda pistons seem to be the better choice out to 79mm as no block decking is required.
Once you start boring to 79mm you end up with a perilously thin sealing surface between the end pairs of bores. This can be helped with offset boring, but there is only so far that you can go before one side of the cylinder wall starts geting a bit thin.

These A series engines were originally designed back in 1965 with a bore of 73mm, so there was plenty of meat between the bores back then, then the factory reduced this surface by 3mm when they went to 76mm bores, & there was no problem, but reducing this sealing surface by 7.65mm when an 80.65mm bore is used is pushing ones luck a bit. Even at a 79mm bore size it becomes necessary to use a figure 8 'O' ring when this mod is performed to improve gasket sealing.

Take it out to 80.65mm & the problems get worse. I am not yet aware of a piston of that size that could be used either, but look foward to learning of it.

The photo is of an A15 with 79mm bores that are centered [not offset bored] & as you can see, it gets a little bit tight in there.
If only the factory had spaced the bores just a leeeetle bit further apart.