Merging 2 Existing sites into MSM

We currently have 2 news sites running on separate instances of Expression Engine.

I want to create a new channel of ‘people profiles’ which ideally will be accessible from both domains/sites. I believe this is possible using the Multi-site manager.

I don’t think this would be an issue if I were building from scratch, so I assume I activate MSM on Site A and then somehow import Site B into the MSM instance.

Is there an established procedure for this? Is this even possible?