Is there a way to copy a Portfolio item and handle it as a post as well?
if I understand you correctly you want to copy the contents of a portfolio project (title, actual content, featured image) to a post. By default there is no such feature in WordPress or Jetpack. I don't know of a plugin, which could do this. I guess if you aren't able to find such a plugin, you'd need to develop one yourself or manually transfer this information to a post.