I acquired a 1984 Nissan Competition Parts catalog at Shasta. Here's what it has on the A12A:

Block:

11010-H2300 A12 BARE BLOCK 73mm/2.87" bore size
11010-H9660 A12A BARE BLOCK 75mm/2.95" bore size
11010-H6200 A13 BARE BLOCK 73mm/2.87" bore size
11010-H9700 A14/A15 BARE BLOCK 76mm/2.99" bore size

So the A12 & A13 share the same bore size. The A14 and A15 likewise share 76mm. The A12A is unique.

Pistons for the A12/A13 (same piston) come in 73, 73.5, and 74mm oversizes. The latter is 0.040" over
Competition Pistons for the A12A/A14 (same piston) come in 76mm. For the A14 only they listed 76.75 and 77mm pistons.

Cranks:
12200-H8515 A12/A12A CRANKSHAFT 70mm/2.76" stroke
12200-H5720 A12 COMPETITION CRANKSHAFT 70mm/2.76" stroke
12200-H8915 A13/A14 CRANKSHAFT 77mm/3.03" stroke
12200-G3400 A15 CRANKSHAFT 82mm/3.23" stroke

Connecting Rods:
12100-H1000 A12 CONNECTING ROD 121.5mm/4.78" center-to-center
12100-H8500 A12A CONNECTING ROD 121.5mm/4.78" center-to-center
12100-H6200 A13 CONNECTING ROD 133mm/5.24" center-to-center
12100-H7200 A14/A15 CONNECTING ROD 133mm/5.24" center-to-center

> The purpose of the question was to find out if it practical to use an A12 crankshaft in an A12A block for a cheap capacity gain

Why not just use the A12A block and the A12A crankshaft for 1237cc? That will definitely work. But the A12A engine block is hard to find anymore, since it was only made in 1979-1982.

Keep in mind that 1971-1973 A12 and 1973-up A12 are the same (1171 cc) but the distributor location and motor mounts changed. We didn't get this newer A12 in the USA.