To use a GoPro on the bottom of the 1030 mount you need one of these:
It's called a Quarter-turn to Friction Flange Mount Adapter and is available from Garmin at the link shown below.
Here is a picture of the 1030 mount with a UT800 light on the bottom, which uses the same mount as a GoPro, attached with this adapter:
Easy peasy.
HTH
Yes, it comes with a hex head bolt.
HTH