OK blokes, here's the deal.

The "genuine" A12 block [from a 1200] will happily bore to 76mm. I have been running the first oversize [76.5mm] for so long that the engine is worn out. There is a 1200 coupe running around here with a 77mm bore [2nd O.S.] & no problems yet. I would not risk any more without a sonic test on the cylinder walls.

Rods
The 76mm [+] pistons have a larger wrist pin & the 1200 rods can be bored. Better yet are the later 120Y type rods. I have a set fron a later type 1200GX engine & they seem to have more meat around the wrist pin area. I have been using the early 1200 rods, bored out, for somewhere near 200,000 miles & no problems yet, but i don't flog my engine like some do.

Pistons.
If you are going to use the 1200 crank, then use the A14 pistons. These will put the piston crown just about flush with the deck of the block.

Better yet, use an A14 srank in the 1200 block. To do this you will need to place the crank in a lathe & machine the dags from it. It is best to have the block bored with at least one piston & rod mock assembled to allow trial fitting.

To pull this off you will need A15 pistons as these have a lower crown & a shorter skirt than the A14. You need to machine the crank to ensure that it does not touch the bottom of the pistons. It doesnt need much.
Next, be carefull about the rod to "bottom of bore" clearance. Some rods have a larger protrusion for the bore oiler than others & these may touch the bottom of the bore, but only just. A small round file on the bottom of the bore fixes that.

You need the A12 length rod with this combo & the A15 pistons come flush with the top of the block.

So what do you get with all this effort? Well with the 77mm bore & the A14 crank combo, you get 1434cc in a rego friendly A12 block.
Thats what the 1200 coupe around here has & it runs like stink. It has an A14 or A15 head [i forget which] that has been modified for the early oiling system & a brace of carbs from a Yamaha FJ1200.

I hope that this has been helpfull.
Chris
P.S.
Please note, this whole engine is built up from stock Datsun "A" engine parts. You pick the cam, the induction & the exhaust that suits your fancy, but the core engine is all stock stuff.