I created a plugin about 6 months ago that does this, but hasn’t had much use. I wouldn’t mind input on it. https://github.com/Hube2/acf-post2post. It will automatically work for posts of the same post type and if a relationship field with the same field name is added to other post types it will work for that as well. If you try it and have question or comments please post create a new issue on github.
