We needed an ACF custom field that lets you pick one or many Gravity Forms to associate with a page. Googling didn’t return anything useful so we decided to write our own. Using the Users Field add-on by Lewis Mcarey as a starting point we had it up an running in no time at all!
You can find the code and installation instructions over on Github – https://github.com/stormuk/Gravity-Forms-ACF-Field.