How to transfer a site from an old engine to a new one painlessly for SEO?

Question

Search Engine Optimization

There is an old site with ugly URLs (like /index.php?id_content=2938&view=news) and a lot of content, as well as good positions and a large number of indexed pages in PS.
Now a new engine is being written for this site. And then it will be necessary to transfer all the content from the old site to the database of the new one, but the CNC will be used on the new engine.
It must be assumed that all pages can fly out of the index when the PS understands that the old urls like: /index.php?id_content=2938&view=news are no more. How to avoid it?
If you generate 301 redirects from old url to CNC address - how will the PS react to this?