All of the methods listed here are generally not recommended. There are two official methods described at
https://cloud.google.com/sdk/:
2. download google-cloud-sdk.zip or google-cloud-sdk.tar.gz, unpack it, and launch the ./google-cloud-sdk/install.sh script.
If you are on CentOS 6, you are correct that it is currently best to install python2.7. We are working on fixing it. After installing python2.7 somewhere, you need to set CLOUDSDK_PYTHON to point to that version of python.
-- Stephen