Is it possible to get the 72 hour transit visa to do so?

I want to enter China from Vietnam overland to visit Kunming via Hekou, instead of flying Hanoi - Beijing - Kunming. We will be visiting Sapa prior to this time, and thought, since we are so close, this would be a fantastic way to get a glimpse of China. I suspect that we might have to apply for a Chinese L type, but wanted to check. Thanks.