A/C for Dino

I am in the middle of the restoration. Hong Kong is hot and sticky, the Dino will not get much use in the summer. I am thinking of installing after market air con but my mechanic said the compressor has to be bolted on to the engine, that means drilling holes on the engine! How was the compressor mounted on the dino that came with a/c? Has anyone installed after market a/c?
Thanks