Going to North Korea through China

Hi I currently live in South Korea and i'm going on a tour of Pyongyang in June, I was planning on sightseeing around Beijing for a few days before but it looks as though I'm not going to be able to get a multiple entry visa. Can you tell me if i do this if it will be ok?

Get a single entry visa spend a few days in Beijing before getting a train to Dandong and then a train into Pyongyang. After Pyongyang come back into China and leave for Seoul within 72 hours from Shenyang airport? Would that work?