Arrive in Guangzhou, going on to Hong Kong

Hi,

If I arrive in Guangzhou from the US, and provide a flight ticket leaving to Hong Kong 2 days later, and apply for a 72 hour transfer visa, can I go to Honk Kong by train, or do I need to go by my original flight ticket?
I wouldn't be traveling out of the Guangdong province if I leave by train.

Please advise.

Thank you,

Alex V.