Moving news and newsletters between hosts with version 3.5.6

[Nomis]

Whilst improving a website I left the old one in place and used a copy of it as a starting point. I have made many improvements but as the old site was still in use, news and newsletters on the new improved site have become out of sync with the "live" site. How do I fix this? I know that I must move something between the two back-end databases but what exactly? I tried updating tl_news in the new sites back-end but only got the new news listings, no content.

[Spooky]

The news content is in tl_content, but it's not easily transferable.

I have made an extension where you can synchronize news archives between different hosts, but it is not publicly available yet.