I would suggest you merging old site with new site.
In this case all content will be accurately duplicated on the new site, we will also set redirect from the old site to new, so you'll avoid duplicates in content (that would negatively influence on ranking).
Once merging is done, we will check all posts and add media items, where needed, fix links.
Would be happy to help with this project as our team has a great experience in merging sites)