Well, at a guess I would say that HC stood for High Compression. Dont forget that there was a lot of poor quality petrol back then, and some areas might only have petrol suitable for Low Compression engines. The Heads were the easiest parts to change, and still are these days.
They hadnt invented the saying Heavy Chevy back then.
But, it could be Heavy Caddy, I suppose.
Bruce,
The Tassie Devil(le),
60 CDV
