The original poster -- rallytwit -- is a seasoned racer. He is looking for flat-tops for A12A engine. He also stated twice that he doesn't want custom pistons, which those D16 pistons are

Unfortunately A10 pistons (73mm bore) won't fit the A12A engine (75mm bore)

In general flat-tops are more powerful than dish pistons given the same compression ratio. For example: 10:1 with dish and small combustion chambers make less power than 10:1 with flatties and medium combustion chambers. They can take more spark advance, return more power and more fuel economy, and are less prone to pinging detonation so can use lower octane fuel. See our tech article Quench

I'd look at Nissan K15 pistons -- off-the-shelf flat-tops, correct pin height and inexpensive. Look like A12 GX flat-tops but with 75.5mm bore