Theres a bunch of varieties of 1.6L Mazda B6 MX5 / Miata pistons. Approx five of them. 8V, 16V, etc. The 1.8L's are no good because the bore became larger. There's also other Mazda pistons plus daewoo, opel, Izuzu pistons that I know of that can be made to fit. Assuming you are going to bore anyway, the pistons height, the bowl volume (if it has a bowl) and the pistons wrist pin (gudgeon pin) are the main concerns.

In addition to the above specs, A10's & A12's have a 17.5mm wrist pin. A12A's, A13's, A14's and A15's all have 19mm pins. When you compare these sizes to those selected by most other manufacturers, the Datsun sizes are uncommon. So, if you want to run MX5 pistons, you must increase the conrod little end from 19mm to 20mm in an A14/15. Other pistons will require different things.

Lets look at an A15 for example: Half the stroke + the conrod length + the piston height = 82/2 + 133 + 30 = 204mm. The block height is 204.1mm. This means the piston at its heighest point is 0.1mm below the deck (gasket). If you vary this figure, you will be changing the compression ratio. Likewise if the piston bowl volume changes. So do your homework first!