The A series engine from 1974 onwards was designed to take an aircon compressor & B310 models were marketed with factory air.
If I remember rightly, you have an A14 in your 1200 so you are set to go.
Find yourself a junk aircon equiped model 210 [B310] & remove ALL of the aircon parts that you can get, including the front pulley on the engine.
You will not be able to use the evaporator unit & will probably need to buy an aftematket under-dash unit, but the compressor assembly, it's mountings, & drive will fit your engine, & you might even be able to use the condenser if you're lucky.
A good aircon shop can make new hoses & pipes as required, & even supply a new condenser if necessary.
Thats the beauty of our Datsuns. A little knowledge of what other models had, a little scrounging & a little cash outlay & you're on your way in aircon luxury.

Good luck