Has anyone attempted to plumb an aircon system into a modified 1200 ute or coupe?......I was hoping to be able to use the stock Silvia compressor & somehow plumb it into the standard 1200 ventilation system?

You can use the compressor & mount that goes with the engine. You will probably need to adapt some condenser & mount it in front of the radiator. As for the evaporator, you will need either an aftermarket unit, or a genuine unit from a donor 1200.
I don't know if there is a factory aircon available for the South African Bakkie, but it might be worth talking to some of our S.A. members. If so, then it might be worth geting the whole heater & aircon assembly from a late model wreck.
I mentioned the heater part as the Bakkie uses a diferent setup & it would be needed for a complete factory instalation inside the cabin.

Hoses can be made by the aircon specialist, so if diferent components have diferent types of fittings, this should not be a problem.