Just an idea. I think it should work as world creation procedure hasn't changed recently.
Find your seed, and create a world with it in the newer version. Locate a pillager outpost in the world and then delete a group of blocks from your real save file where that area is, a lot of vids on the internet show how this is done, in particular Pixlriffs has a good one about it. Make sure you make a backup before doing this. When you again revisit that area the new version should recreate it wit all structures.
Haven;t tried this myself so beware.