I originally bored my 1200GX engine to 76mm & used A14 pistons. That only lasted about 100,000 miles, so i bored it again, this time to the first oversize for the A14, which is 76.5mm. This too lasted only a paltry 100,000 miles, so i will be boring it yet again to the next oversize of 77mm. With care, it should last for the rest of my driving lifetime.

there is already a 1200 coupe running around here with the original type 1200 engine at 77mm.
Nissan at one time produced a 76.8mm forged piston for racing use, for use in the A12 engine, so you should be safe at 76mm & i, personally, wouldnt hesitate to go to 76.5mm.
Chris