Quote: Yes, Nissan Competition sold the same flattop piston for use in A12 or in 1974 A13 engine.

12010-H2361 73MM/2.874" PISTON
[This is the factory stock GX piston]

Both A12 and 1974 A13 are 73 mm diameter, pin height 32.5 mm, pin diameter 17.45 mm. The A13 rod differs from the A14 rod.

The part numbers are not the same for A12 and 1974 A13 piston. I would guess the dish on the A13 piston is larger, so as to keep the same compression ratio. So using the 1971 A12 piston may bump up the compression to 9.5:1 and using the 1972-1973 A12 piston to 9.0:1. Still good for regular gasoline.