Flying to HK via Guangzhou

I am wondering if I still qualify for the 72 hour free transit if I buy a one way ticket from Seoul to Guangzhou and a one way ticket to Hong Kong leaving Guangzhou two days later.

Even though those flights are not part of a single booking, would it still be possible to get the transit visa?

Also, if the GZ free transit provides access to the whole province, would it be possible to leave Guangzhou via train to go to HK instead of flying?