Welcome Ryan- congrats on your purchase of a hybrid Z. Did the previous owner give you any details on the LT1 swap? Specifically, did the conversion include a way to get the factory BCM, ABS and NATS system to actually function? Many conversions simply disable these factory systems and allow the engine to function with only the most basic systems.
That's why the factory locking system (which is incorporated in the BCM) and tach don't function. Getting them back won't be cheap or easy, but understanding how this conversion was done is the first step. For a custom a/c unit, I think you'd be better off taking it to a specialist shop and having them give you an estimate of what it'd take.