what about entry to Guanzhou by train holding Australia passport 72hrs transit visa eligible

Grace, 72 hours free transit is eligible only when you fly in and fly out of China within 72 hours transit. You can't make use of 72 hours free transit if you take a train from HK to Guangzhou. Since you stay for two nights, you may not apply for 24 hours transit as well. So I think you should apply for a L type.