Both v4 and v3 could live together as independent programs on your site, and they will show the same data from the Program Event Framework of Open Y
On the screenshot above you can see Open Y components in a list for both Activity Finder v3 and v4
In order to create v3 Activity Finder application you need to create 2 landing pages, referencing each other, one with Activity Finder [deprecated], another one with Activity Finder Search [deprecated]
See
See
In order to create v4 Activity Finder application, you need to create 1 landing page, with the Activity Finder component on it
See sandbox