Should I contact a few professors about being interested in pursuing the PhD part of my MD-PhD in their lab? I am very sure about the department I want to join for my PhD. I know that people contact PIs for PhD programs and didn't know if that was common practice for the MD-PhD as well.
As an MD/PhD you are still a PhD, so what applies to PhD students applies to you. If you connect with potential PIs before applying, you can then possibly include in your secondary application (especially for the "Why this school?" question) that you are interested in a certain lab or labs and have corresponded with the PI(s). It can show that you're serious about attending the school, which will definitely help!