If you have an A12, & being in the US I presume it's the 1200 engine [front dist.] then you can source the 77mm pistond from your friendly Nissan parts counter or from a national parts supplier. They are the second oversize for the A14 engine which is 76mm standard, so two oversizes at a half mill each makes it 77.

The downside is that they use a larger wrist pin diameter which can be fixed in one of two ways.

Method A. Have the rods machined out in the small end. This is what I did 25 years ago when I ran a big bore in my 1200 engine.
Method B. Source a set of rods from the A12A that was used in some US model 210's [B310] These are the right length & have the right small end diameter, but use pistons of 75mm diameter.

It looks like you're cutting it fine with the 1300 class as 77mm will yeild 1303.855cc while your preffered size of 76.85mm would yeild 1298.78cc.