Synchronisation is not the right concept for it.
Here is a post that describes the technique I am referring to that can be used to integrate multiple projects together.
There are downsides of course, searches need to be run more than once if you don’t know where something is at all, but a “meta project” that does that as part of its function—helps you find where things are and can be embellished and made better as you find yourself looking for things—is part of the idea here.