I have just picked up the XD I have wanted for so long and like a lot the air con is not working. It is a Ghia so had it originally and it came with the compressor etc. I have a gut feeling that I'm better off replacing with a newer system. It's a 351c, c4 auto.

Replace all the hoses (R134A spec), the TX Valve (again, R134A spec ), see if the thermostat still works okay, and replace the compressor with a Sanden 506 or 508....and a new Reciever/Drier.
Then it will need to be pressure tested for leaks before being gassed up for service.