Do I even need to rebuild the carb?

I have a '72 Chevy Impala. It's got a new engine and trans. but it's been sitting for a while (at least a year and a half). No one really drove it in my family and I've inherited it. Gas has been sitting in it, and I know that I must drain the gas tank and fuel lines, because the gas has probably turned to varnish. There was gas in it while the carb sat. so, what I want to know is if I have to rebuild it. I've heard some things about seeing if it'll start first, but I've also heard that if it needs to get rebuilt that can damage the engine. Can anyone help, please?