You pretty much leave the 1200 loom alone. You can chop off the couple of wires that went on the A12. You use the 1200 loom to trigger the starter motor. That should go straight on (it's a single spade). You can also wire the CA alternator into the standard loom where the original one's fat 12V wire is (I think it's white with red tracer). You need to splice into the datsun loom for the ignition relay trigger. You can, although I don't think it's essential, splice into the cranking 12v signal in the original loom for the signal to the CA computer as it has an input for cranking 12v.

I think that's pretty much it.