this is in the tech section:
A14 Round-port head
Intake: 37mm
Exhaust: 30mm
Has round intake ports (like the A12 head). Casting numbers are under the valve cover area: "990" towards the rear and "454" towards the front. This is the head used on A12As and some A14s. These cannot be ported out to match the oval port heads (you'll hit a water jacket). These can be found on some late A14s, like 1980. It has two small coolant holes below the intake ports, to provide heat for the intake manifold. These came on the "GFU" and "MPG" cars (USA-market B210 and B310 fuel economy champion models).

as opposed to:
A14 Oval-port "H72" head
Intake: 37mm
Exhaust: 30mm
Somtimes called the "low compression GX head", it has a casting number "H72". Has a larger 360 degree "open" combustion chamber for lower compression ratios. It does not have the coolant holes below the intake ports. The H72 head was common around 1977-1978. This H72 head is basically the same as the Nissan competition GX head, but it has a lower compression combustion chamber, and the same regular size valves as any other A-series head. It has the nice straight big oval intake ports. It is better than the A15 oval "swirl port" head, and certainly better than the round intake port A14 heads. EGR port in the exhaust ports. These can be milled .080" or more to raise compression.

which can be compared to your A12 head:
A12 round-port head (1971-1973 Datsun 1200)
Intake: 35mm
Exhaust: 29mm
compression ratio 9.0:1 with dished pistons
A ported and polished standard A12 head with larger valves fitted flows about the same as a standard GX head. Also see head trivia.The A12 heads and later head provided oil to the rocker armshafts in different locations so you may need to redrill the oil passage.

so, it all depends on if you want low torque power or high rpm power as to what head you use.. but yes, fitting any A14 head will be of benefit to your A12.